Make examples consistently use 4-space indentation.
Use \file{} for file names.
Prefer \code{blat} and \emph{blat} to {\tt blat} and {\em blat}; this matches
current style in the Library Reference a bit better.
Made the example startup banner current. The version number should be
bumped before the next release.
diff --git a/Doc/tut.tex b/Doc/tut.tex
index 0afcb3f..a3d8da8 100644
--- a/Doc/tut.tex
+++ b/Doc/tut.tex
@@ -42,8 +42,8 @@
Python interpreter handy for hands-on experience, but as the examples
are self-contained, the tutorial can be read off-line as well.
-For a description of standard objects and modules, see the {\em Python
-Library Reference} document. The {\em Python Reference Manual} gives
+For a description of standard objects and modules, see the \emph{Python
+Library Reference} document. The \emph{Python Reference Manual} gives
a more formal definition of the language.
\end{abstract}
@@ -104,12 +104,12 @@
simple to use, but it is a real programming language, offering much
more structure and support for large programs than the shell has. On
the other hand, it also offers much more error checking than C, and,
-being a {\em very-high-level language}, it has high-level data types
+being a \emph{very-high-level language}, it has high-level data types
built in, such as flexible arrays and dictionaries that would cost you
days to implement efficiently in C. Because of its more general data
-types Python is applicable to a much larger problem domain than {\em
-Awk} or even {\em Perl}, yet many things are at least as easy in
-Python as in those languages.
+types Python is applicable to a much larger problem domain than
+\emph{Awk} or even \emph{Perl}, yet many things are at least as easy
+in Python as in those languages.
Python allows you to split up your program in modules that can be
reused in other Python programs. It comes with a large collection of
@@ -139,7 +139,7 @@
no variable or argument declarations are necessary.
\end{itemize}
-Python is {\em extensible}: if you know how to program in C it is easy
+Python is \emph{extensible}: if you know how to program in C it is easy
to add a new built-in function or module to the interpreter, either to
perform critical operations at maximum speed, or to link Python
programs to libraries that may only be available in binary form (such
@@ -172,8 +172,8 @@
\section{Invoking the Interpreter}
-The Python interpreter is usually installed as {\tt /usr/local/bin/python}
-on those machines where it is available; putting {\tt /usr/local/bin} in
+The Python interpreter is usually installed as \file{/usr/local/bin/python}
+on those machines where it is available; putting \file{/usr/local/bin} in
your \UNIX{} shell's search path makes it possible to start it by
typing the command
@@ -183,8 +183,8 @@
%
to the shell. Since the choice of the directory where the interpreter
lives is an installation option, other places are possible; check with
-your local Python guru or system administrator. (E.g., {\tt
-/usr/local/python} is a popular alternative location.)
+your local Python guru or system administrator. (E.g.,
+\file{/usr/local/python} is a popular alternative location.)
Typing an EOF character (Control-D on \UNIX{}, Control-Z or F6 on DOS
or Windows) at the primary prompt causes the interpreter to exit with
@@ -199,27 +199,27 @@
quickest check to see whether command line editing is supported is
typing Control-P to the first Python prompt you get. If it beeps, you
have command line editing; see Appendix A for an introduction to the
-keys. If nothing appears to happen, or if \verb/^P/ is echoed,
+keys. If nothing appears to happen, or if \code{\^P} is echoed,
command line editing isn't available; you'll only be able to use
backspace to remove characters from the current line.
The interpreter operates somewhat like the \UNIX{} shell: when called
with standard input connected to a tty device, it reads and executes
commands interactively; when called with a file name argument or with
-a file as standard input, it reads and executes a {\em script} from
+a file as standard input, it reads and executes a \emph{script} from
that file.
A third way of starting the interpreter is
-``{\tt python -c command [arg] ...}'', which
-executes the statement(s) in {\tt command}, analogous to the shell's
-{\tt -c} option. Since Python statements often contain spaces or other
-characters that are special to the shell, it is best to quote {\tt
-command} in its entirety with double quotes.
+\samp{python -c command [arg] ...}, which
+executes the statement(s) in \code{command}, analogous to the shell's
+\code{-c} option. Since Python statements often contain spaces or other
+characters that are special to the shell, it is best to quote
+\code{command} in its entirety with double quotes.
-Note that there is a difference between ``{\tt python file}'' and
-``{\tt python <file}''. In the latter case, input requests from the
-program, such as calls to {\tt input()} and {\tt raw_input()}, are
-satisfied from {\em file}. Since this file has already been read
+Note that there is a difference between \samp{python file} and
+\samp{python <file}. In the latter case, input requests from the
+program, such as calls to \code{input()} and \code{raw_input()}, are
+satisfied from \emph{file}. Since this file has already been read
until the end by the parser before the program starts executing, the
program will encounter EOF immediately. In the former case (which is
usually what you want) they are satisfied from whatever file or device
@@ -227,39 +227,39 @@
When a script file is used, it is sometimes useful to be able to run
the script and enter interactive mode afterwards. This can be done by
-passing {\tt -i} before the script. (This does not work if the script
+passing \code{-i} before the script. (This does not work if the script
is read from standard input, for the same reason as explained in the
previous paragraph.)
\subsection{Argument Passing}
When known to the interpreter, the script name and additional
-arguments thereafter are passed to the script in the variable {\tt
-sys.argv}, which is a list of strings. Its length is at least one;
-when no script and no arguments are given, {\tt sys.argv[0]} is an
-empty string. When the script name is given as {\tt '-'} (meaning
-standard input), {\tt sys.argv[0]} is set to {\tt '-'}. When {\tt -c
-command} is used, {\tt sys.argv[0]} is set to {\tt '-c'}. Options
-found after {\tt -c command} are not consumed by the Python
-interpreter's option processing but left in {\tt sys.argv} for the
+arguments thereafter are passed to the script in the variable
+\code{sys.argv}, which is a list of strings. Its length is at least
+one; when no script and no arguments are given, \code{sys.argv[0]} is
+an empty string. When the script name is given as \code{'-'} (meaning
+standard input), \code{sys.argv[0]} is set to \code{'-'}. When \code{-c
+command} is used, \code{sys.argv[0]} is set to \code{'-c'}. Options
+found after \code{-c command} are not consumed by the Python
+interpreter's option processing but left in \code{sys.argv} for the
command to handle.
\subsection{Interactive Mode}
When commands are read from a tty, the interpreter is said to be in
-{\em interactive\ mode}. In this mode it prompts for the next command
-with the {\em primary\ prompt}, usually three greater-than signs ({\tt
->>>}); for continuation lines it prompts with the
-{\em secondary\ prompt},
-by default three dots ({\tt ...}).
+\emph{interactive mode}. In this mode it prompts for the next command
+with the \emph{primary prompt}, usually three greater-than signs
+(\code{>>>}); for continuation lines it prompts with the
+\emph{secondary prompt},
+by default three dots (\code{...}).
The interpreter prints a welcome message stating its version number
and a copyright notice before printing the first prompt, e.g.:
\bcode\begin{verbatim}
python
-Python 1.4 (Oct 25 1996) [GCC 2.7.2]
-Copyright 1991-1996 Stichting Mathematisch Centrum, Amsterdam
+Python 1.5b1 (#1, Dec 3 1997, 00:02:06) [GCC 2.7.2.2] on sunos5
+Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
>>>
\end{verbatim}\ecode
@@ -271,8 +271,8 @@
message and a stack trace. In interactive mode, it then returns to
the primary prompt; when input came from a file, it exits with a
nonzero exit status after printing
-the stack trace. (Exceptions handled by an {\tt except} clause in a
-{\tt try} statement are not errors in this context.) Some errors are
+the stack trace. (Exceptions handled by an \code{except} clause in a
+\code{try} statement are not errors in this context.) Some errors are
unconditionally fatal and cause an exit with a nonzero exit; this
applies to internal inconsistencies and some cases of running out of
memory. All error messages are written to the standard error stream;
@@ -285,9 +285,9 @@
\footnote{
A problem with the GNU Readline package may prevent this.
}
-Typing an interrupt while a command is executing raises the {\tt
-KeyboardInterrupt} exception, which may be handled by a {\tt try}
-statement.
+Typing an interrupt while a command is executing raises the
+\code{KeyboardInterrupt} exception, which may be handled by a
+\code{try} statement.
\subsection{Executable Python scripts}
@@ -299,7 +299,7 @@
\end{verbatim}\ecode
%
(assuming that the interpreter is on the user's PATH) at the beginning
-of the script and giving the file an executable mode. The {\tt \#!}
+of the script and giving the file an executable mode. The \code{\#!}
must be the first two characters of the file.
\subsection{The Interactive Startup File}
@@ -309,30 +309,30 @@
When you use Python interactively, it is frequently handy to have some
standard commands executed every time the interpreter is started. You
-can do this by setting an environment variable named {\tt
-PYTHONSTARTUP} to the name of a file containing your start-up
-commands. This is similar to the {\tt .profile} feature of the \UNIX{}
+can do this by setting an environment variable named
+\code{PYTHONSTARTUP} to the name of a file containing your start-up
+commands. This is similar to the \file{.profile} feature of the \UNIX{}
shells.
This file is only read in interactive sessions, not when Python reads
-commands from a script, and not when {\tt /dev/tty} is given as the
+commands from a script, and not when \file{/dev/tty} is given as the
explicit source of commands (which otherwise behaves like an
interactive session). It is executed in the same name space where
interactive commands are executed, so that objects that it defines or
imports can be used without qualification in the interactive session.
-You can also change the prompts {\tt sys.ps1} and {\tt sys.ps2} in
+You can also change the prompts \code{sys.ps1} and \code{sys.ps2} in
this file.
If you want to read an additional start-up file from the current
directory, you can program this in the global start-up file, e.g.
-\verb\execfile('.pythonrc')\. If you want to use the startup file
+\code{execfile('.pythonrc')}. If you want to use the startup file
in a script, you must write this explicitly in the script, e.g.
-\verb\import os;\ \verb\execfile(os.environ['PYTHONSTARTUP'])\.
+\code{import os;} \code{execfile(os.environ['PYTHONSTARTUP'])}.
\chapter{An Informal Introduction to Python}
In the following examples, input and output are distinguished by the
-presence or absence of prompts ({\tt >>>} and {\tt ...}): to repeat
+presence or absence of prompts (\code{>>>} and \code{...}): to repeat
the example, you must type everything after the prompt, when the
prompt appears; lines that do not begin with a prompt are output from
the interpreter.%
@@ -347,13 +347,13 @@
\section{Using Python as a Calculator}
Let's try some simple Python commands. Start the interpreter and wait
-for the primary prompt, {\tt >>>}. (It shouldn't take long.)
+for the primary prompt, \code{>>>}. (It shouldn't take long.)
\subsection{Numbers}
The interpreter acts as a simple calculator: you can type an
expression at it and it will write the value. Expression syntax is
-straightforward: the operators {\tt +}, {\tt -}, {\tt *} and {\tt /}
+straightforward: the operators \code{+}, \code{-}, \code{*} and \code{/}
work just like in most other languages (e.g., Pascal or C); parentheses
can be used for grouping. For example:
@@ -375,7 +375,7 @@
>>>
\end{verbatim}\ecode
%
-Like in C, the equal sign ({\tt =}) is used to assign a value to a
+Like in C, the equal sign (\code{=}) is used to assign a value to a
variable. The value of an assignment is not written:
\bcode\begin{verbatim}
@@ -542,11 +542,11 @@
funny characters escaped by backslashes, to show the precise
value. The string is enclosed in double quotes if the string contains
a single quote and no double quotes, else it's enclosed in single
-quotes. (The {\tt print} statement, described later, can be used to
+quotes. (The \code{print} statement, described later, can be used to
write strings without quotes or escapes.)
-Strings can be concatenated (glued together) with the {\tt +}
-operator, and repeated with {\tt *}:
+Strings can be concatenated (glued together) with the \code{+}
+operator, and repeated with \code{*}:
\bcode\begin{verbatim}
>>> word = 'Help' + 'A'
@@ -564,7 +564,7 @@
Strings can be subscripted (indexed); like in C, the first character
of a string has subscript (index) 0. There is no separate character
type; a character is simply a string of size one. Like in Icon,
-substrings can be specified with the {\em slice} notation: two indices
+substrings can be specified with the \emph{slice} notation: two indices
separated by a colon.
\bcode\begin{verbatim}
@@ -589,8 +589,8 @@
>>>
\end{verbatim}\ecode
%
-Here's a useful invariant of slice operations: \verb\s[:i] + s[i:]\
-equals \verb\s\.
+Here's a useful invariant of slice operations: \code{s[:i] + s[i:]}
+equals \code{s}.
\bcode\begin{verbatim}
>>> word[:2] + word[2:]
@@ -652,9 +652,9 @@
\end{verbatim}\ecode
%
The best way to remember how slices work is to think of the indices as
-pointing {\em between} characters, with the left edge of the first
+pointing \emph{between} characters, with the left edge of the first
character numbered 0. Then the right edge of the last character of a
-string of {\tt n} characters has index {\tt n}, for example:
+string of \var{n} characters has index \var{n}, for example:
\bcode\begin{verbatim}
+---+---+---+---+---+
@@ -666,14 +666,14 @@
%
The first row of numbers gives the position of the indices 0...5 in
the string; the second row gives the corresponding negative indices.
-The slice from \verb\i\ to \verb\j\ consists of all characters between
-the edges labeled \verb\i\ and \verb\j\, respectively.
+The slice from \var{i} to \var{j} consists of all characters between
+the edges labeled \var{i} and \var{j}, respectively.
For nonnegative indices, the length of a slice is the difference of
the indices, if both are within bounds, e.g., the length of
-\verb\word[1:3]\ is 2.
+\code{word[1:3]} is 2.
-The built-in function {\tt len()} returns the length of a string:
+The built-in function \code{len()} returns the length of a string:
\bcode\begin{verbatim}
>>> s = 'supercalifragilisticexpialidocious'
@@ -684,8 +684,8 @@
\subsection{Lists}
-Python knows a number of {\em compound} data types, used to group
-together other values. The most versatile is the {\em list}, which
+Python knows a number of \emph{compound} data types, used to group
+together other values. The most versatile is the \emph{list}, which
can be written as a list of comma-separated values (items) between
square brackets. List items need not all have the same type.
@@ -715,7 +715,7 @@
>>>
\end{verbatim}\ecode
%
-Unlike strings, which are {\em immutable}, it is possible to change
+Unlike strings, which are \emph{immutable}, it is possible to change
individual elements of a list:
\bcode\begin{verbatim}
@@ -749,7 +749,7 @@
>>>
\end{verbatim}\ecode
%
-The built-in function {\tt len()} also applies to lists:
+The built-in function \code{len()} also applies to lists:
\bcode\begin{verbatim}
>>> len(a)
@@ -777,14 +777,14 @@
>>>
\end{verbatim}\ecode
%
-Note that in the last example, {\tt p[1]} and {\tt q} really refer to
-the same object! We'll come back to {\em object semantics} later.
+Note that in the last example, \code{p[1]} and \code{q} really refer to
+the same object! We'll come back to \emph{object semantics} later.
\section{First Steps Towards Programming}
Of course, we can use Python for more complicated tasks than adding
two and two together. For instance, we can write an initial
-subsequence of the {\em Fibonacci} series as follows:
+subsequence of the \emph{Fibonacci} series as follows:
\bcode\begin{verbatim}
>>> # Fibonacci series:
@@ -808,23 +808,23 @@
\begin{itemize}
\item
-The first line contains a {\em multiple assignment}: the variables
-{\tt a} and {\tt b} simultaneously get the new values 0 and 1. On the
+The first line contains a \emph{multiple assignment}: the variables
+\code{a} and \code{b} simultaneously get the new values 0 and 1. On the
last line this is used again, demonstrating that the expressions on
the right-hand side are all evaluated first before any of the
assignments take place.
\item
-The {\tt while} loop executes as long as the condition (here: {\tt b <
+The \code{while} loop executes as long as the condition (here: \code{b <
10}) remains true. In Python, like in C, any non-zero integer value is
true; zero is false. The condition may also be a string or list value,
in fact any sequence; anything with a non-zero length is true, empty
sequences are false. The test used in the example is a simple
comparison. The standard comparison operators are written the same as
-in C: {\tt <}, {\tt >}, {\tt ==}, {\tt <=}, {\tt >=} and {\tt !=}.
+in C: \code{<}, \code{>}, \code{==}, \code{<=}, \code{>=} and \code{!=}.
\item
-The {\em body} of the loop is {\em indented}: indentation is Python's
+The \emph{body} of the loop is \emph{indented}: indentation is Python's
way of grouping statements. Python does not (yet!) provide an
intelligent input line editing facility, so you have to type a tab or
space(s) for each indented line. In practice you will prepare more
@@ -835,7 +835,7 @@
line).
\item
-The {\tt print} statement writes the value of the expression(s) it is
+The \code{print} statement writes the value of the expression(s) it is
given. It differs from just writing the expression you want to write
(as we did earlier in the calculator examples) in the way it handles
multiple expressions and strings. Strings are printed without quotes,
@@ -869,13 +869,13 @@
\chapter{More Control Flow Tools}
-Besides the {\tt while} statement just introduced, Python knows the
+Besides the \code{while} statement just introduced, Python knows the
usual control flow statements known from other languages, with some
twists.
\section{If Statements}
-Perhaps the most well-known statement type is the {\tt if} statement.
+Perhaps the most well-known statement type is the \code{if} statement.
For example:
\bcode\begin{verbatim}
@@ -891,20 +891,20 @@
...
\end{verbatim}\ecode
%
-There can be zero or more {\tt elif} parts, and the {\tt else} part is
-optional. The keyword `{\tt elif}' is short for `{\tt else if}', and is
-useful to avoid excessive indentation. An {\tt if...elif...elif...}
-sequence is a substitute for the {\em switch} or {\em case} statements
+There can be zero or more \code{elif} parts, and the \code{else} part is
+optional. The keyword `\code{elif}' is short for `\code{else if}', and is
+useful to avoid excessive indentation. An \code{if...elif...elif...}
+sequence is a substitute for the \emph{switch} or \emph{case} statements
found in other languages.
\section{For Statements}
-The {\tt for} statement in Python differs a bit from what you may be
+The \code{for} statement in Python differs a bit from what you may be
used to in C or Pascal. Rather than always iterating over an
arithmetic progression of numbers (like in Pascal), or leaving the user
-completely free in the iteration test and step (as C), Python's {\tt
-for} statement iterates over the items of any sequence (e.g., a list
-or a string), in the order that they appear in the sequence. For
+completely free in the iteration test and step (as C), Python's
+\code{for} statement iterates over the items of any sequence (e.g., a
+list or a string), in the order that they appear in the sequence. For
example (no pun intended):
\bcode\begin{verbatim}
@@ -934,10 +934,10 @@
>>>
\end{verbatim}\ecode
-\section{The {\tt range()} Function}
+\section{The \sectcode{range()} Function}
If you do need to iterate over a sequence of numbers, the built-in
-function {\tt range()} comes in handy. It generates lists containing
+function \code{range()} comes in handy. It generates lists containing
arithmetic progressions, e.g.:
\bcode\begin{verbatim}
@@ -946,7 +946,7 @@
>>>
\end{verbatim}\ecode
%
-The given end point is never part of the generated list; {\tt range(10)}
+The given end point is never part of the generated list; \code{range(10)}
generates a list of 10 values, exactly the legal indices for items of a
sequence of length 10. It is possible to let the range start at another
number, or to specify a different increment (even negative):
@@ -961,8 +961,8 @@
>>>
\end{verbatim}\ecode
%
-To iterate over the indices of a sequence, combine {\tt range()} and
-{\tt len()} as follows:
+To iterate over the indices of a sequence, combine \code{range()} and
+\code{len()} as follows:
\bcode\begin{verbatim}
>>> a = ['Mary', 'had', 'a', 'little', 'lamb']
@@ -979,16 +979,16 @@
\section{Break and Continue Statements, and Else Clauses on Loops}
-The {\tt break} statement, like in C, breaks out of the smallest
-enclosing {\tt for} or {\tt while} loop.
+The \code{break} statement, like in C, breaks out of the smallest
+enclosing \code{for} or \code{while} loop.
-The {\tt continue} statement, also borrowed from C, continues with the
+The \code{continue} statement, also borrowed from C, continues with the
next iteration of the loop.
-Loop statements may have an {\tt else} clause; it is executed when the
-loop terminates through exhaustion of the list (with {\tt for}) or when
-the condition becomes false (with {\tt while}), but not when the loop is
-terminated by a {\tt break} statement. This is exemplified by the
+Loop statements may have an \code{else} clause; it is executed when the
+loop terminates through exhaustion of the list (with \code{for}) or when
+the condition becomes false (with \code{while}), but not when the loop is
+terminated by a \code{break} statement. This is exemplified by the
following loop, which searches for prime numbers:
\bcode\begin{verbatim}
@@ -1013,7 +1013,7 @@
\section{Pass Statements}
-The {\tt pass} statement does nothing.
+The \code{pass} statement does nothing.
It can be used when a statement is required syntactically but the
program requires no action.
For example:
@@ -1034,8 +1034,8 @@
... "Print a Fibonacci series up to n"
... a, b = 0, 1
... while b < n:
-... print b,
-... a, b = b, a+b
+... print b,
+... a, b = b, a+b
...
>>> # Now call the function we just defined:
... fib(2000)
@@ -1043,7 +1043,7 @@
>>>
\end{verbatim}\ecode
%
-The keyword {\tt def} introduces a function {\em definition}. It must
+The keyword \code{def} introduces a function \emph{definition}. It must
be followed by the function name and the parenthesized list of formal
parameters. The statements that form the body of the function start
at the next line, indented by a tab stop. The first statement of the
@@ -1054,21 +1054,21 @@
it's good practice to include docstrings in code that you write, so
try to make a habit of it.
-The {\em execution} of a function introduces a new symbol table used
+The \emph{execution} of a function introduces a new symbol table used
for the local variables of the function. More precisely, all variable
assignments in a function store the value in the local symbol table;
whereas variable references first look in the local symbol table, then
in the global symbol table, and then in the table of built-in names.
Thus,
global variables cannot be directly assigned a value within a
-function (unless named in a {\tt global} statement), although
+function (unless named in a \code{global} statement), although
they may be referenced.
The actual parameters (arguments) to a function call are introduced in
the local symbol table of the called function when it is called; thus,
-arguments are passed using {\em call\ by\ value}.%
+arguments are passed using \emph{call by value}.%
\footnote{
- Actually, {\em call by object reference} would be a better
+ Actually, \emph{call by object reference} would be a better
description, since if a mutable object is passed, the caller
will see any changes the callee makes to it (e.g., items
inserted into a list).
@@ -1094,11 +1094,11 @@
>>>
\end{verbatim}\ecode
%
-You might object that {\tt fib} is not a function but a procedure. In
+You might object that \code{fib} is not a function but a procedure. In
Python, like in C, procedures are just functions that don't return a
value. In fact, technically speaking, procedures do return a value,
-albeit a rather boring one. This value is called {\tt None} (it's a
-built-in name). Writing the value {\tt None} is normally suppressed by
+albeit a rather boring one. This value is called \code{None} (it's a
+built-in name). Writing the value \code{None} is normally suppressed by
the interpreter if it would be the only value written. You can see it
if you really want to:
@@ -1117,8 +1117,8 @@
... result = []
... a, b = 0, 1
... while b < n:
-... result.append(b) # see below
-... a, b = b, a+b
+... result.append(b) # see below
+... a, b = b, a+b
... return result
...
>>> f100 = fib2(100) # call it
@@ -1132,25 +1132,25 @@
\begin{itemize}
\item
-The {\tt return} statement returns with a value from a function. {\tt
-return} without an expression argument is used to return from the middle
-of a procedure (falling off the end also returns from a procedure), in
-which case the {\tt None} value is returned.
+The \code{return} statement returns with a value from a function.
+\code{return} without an expression argument is used to return from
+the middle of a procedure (falling off the end also returns from a
+procedure), in which case the \code{None} value is returned.
\item
-The statement {\tt result.append(b)} calls a {\em method} of the list
-object {\tt result}. A method is a function that `belongs' to an
-object and is named {\tt obj.methodname}, where {\tt obj} is some
-object (this may be an expression), and {\tt methodname} is the name
+The statement \code{result.append(b)} calls a \emph{method} of the list
+object \code{result}. A method is a function that `belongs' to an
+object and is named \code{obj.methodname}, where \code{obj} is some
+object (this may be an expression), and \code{methodname} is the name
of a method that is defined by the object's type. Different types
define different methods. Methods of different types may have the
same name without causing ambiguity. (It is possible to define your
-own object types and methods, using {\em classes}, as discussed later
+own object types and methods, using \emph{classes}, as discussed later
in this tutorial.)
-The method {\tt append} shown in the example, is defined for
+The method \code{append} shown in the example, is defined for
list objects; it adds a new element at the end of the list. In this
example
-it is equivalent to {\tt result = result + [b]}, but more efficient.
+it is equivalent to \code{result = result + [b]}, but more efficient.
\end{itemize}
@@ -1166,31 +1166,31 @@
arguments than it is defined, e.g.
\begin{verbatim}
- def ask_ok(prompt, retries = 4, complaint = 'Yes or no, please!'):
- while 1:
- ok = raw_input(prompt)
- if ok in ('y', 'ye', 'yes'): return 1
- if ok in ('n', 'no', 'nop', 'nope'): return 0
- retries = retries - 1
- if retries < 0: raise IOError, 'refusenik user'
- print complaint
+ def ask_ok(prompt, retries=4, complaint='Yes or no, please!'):
+ while 1:
+ ok = raw_input(prompt)
+ if ok in ('y', 'ye', 'yes'): return 1
+ if ok in ('n', 'no', 'nop', 'nope'): return 0
+ retries = retries - 1
+ if retries < 0: raise IOError, 'refusenik user'
+ print complaint
\end{verbatim}
This function can be called either like this:
-\verb\ask_ok('Do you really want to quit?')\ or like this:
-\verb\ask_ok('OK to overwrite the file?', 2)\.
+\code{ask_ok('Do you really want to quit?')} or like this:
+\code{ask_ok('OK to overwrite the file?', 2)}.
The default values are evaluated at the point of function definition
-in the {\em defining} scope, so that e.g.
+in the \emph{defining} scope, so that e.g.
\begin{verbatim}
- i = 5
- def f(arg = i): print arg
- i = 6
- f()
+ i = 5
+ def f(arg = i): print arg
+ i = 6
+ f()
\end{verbatim}
-will print \verb\5\.
+will print \code{5}.
\subsection{Keyword Arguments}
@@ -1280,8 +1280,8 @@
of arguments, zero or more normal arguments may occur.
\begin{verbatim}
- def fprintf(file, format, *args):
- file.write(format % args)
+ def fprintf(file, format, *args):
+ file.write(format % args)
\end{verbatim}
\chapter{Data Structures}
@@ -1296,31 +1296,31 @@
\begin{description}
-\item[{\tt insert(i, x)}]
+\item[\code{insert(i, x)}]
Insert an item at a given position. The first argument is the index of
-the element before which to insert, so {\tt a.insert(0, x)} inserts at
-the front of the list, and {\tt a.insert(len(a), x)} is equivalent to
-{\tt a.append(x)}.
+the element before which to insert, so \code{a.insert(0, x)} inserts at
+the front of the list, and \code{a.insert(len(a), x)} is equivalent to
+\code{a.append(x)}.
-\item[{\tt append(x)}]
-Equivalent to {\tt a.insert(len(a), x)}.
+\item[\code{append(x)}]
+Equivalent to \code{a.insert(len(a), x)}.
-\item[{\tt index(x)}]
-Return the index in the list of the first item whose value is {\tt x}.
+\item[\code{index(x)}]
+Return the index in the list of the first item whose value is \code{x}.
It is an error if there is no such item.
-\item[{\tt remove(x)}]
-Remove the first item from the list whose value is {\tt x}.
+\item[\code{remove(x)}]
+Remove the first item from the list whose value is \code{x}.
It is an error if there is no such item.
-\item[{\tt sort()}]
+\item[\code{sort()}]
Sort the items of the list, in place.
-\item[{\tt reverse()}]
+\item[\code{reverse()}]
Reverse the elements of the list, in place.
-\item[{\tt count(x)}]
-Return the number of times {\tt x} appears in the list.
+\item[\code{count(x)}]
+Return the number of times \code{x} appears in the list.
\end{description}
@@ -1351,31 +1351,31 @@
\subsection{Functional Programming Tools}
There are three built-in functions that are very useful when used with
-lists: \verb\filter\, \verb\map\, and \verb\reduce\.
+lists: \code{filter()}, \code{map()}, and \code{reduce()}.
-\verb\filter(function, sequence)\ returns a sequence (of the same
+\code{filter(function, sequence)} returns a sequence (of the same
type, if possible) consisting of those items from the sequence for
-which \verb\function(item)\ is true. For example, to compute some
+which \code{function(item)} is true. For example, to compute some
primes:
\begin{verbatim}
- >>> def f(x): return x%2 != 0 and x%3 != 0
- ...
- >>> filter(f, range(2, 25))
- [5, 7, 11, 13, 17, 19, 23]
- >>>
+ >>> def f(x): return x%2 != 0 and x%3 != 0
+ ...
+ >>> filter(f, range(2, 25))
+ [5, 7, 11, 13, 17, 19, 23]
+ >>>
\end{verbatim}
-\verb\map(function, sequence)\ calls \verb\function(item)\ for each of
+\code{map(function, sequence)} calls \code{function(item)} for each of
the sequence's items and returns a list of the return values. For
example, to compute some cubes:
\begin{verbatim}
- >>> def cube(x): return x*x*x
- ...
- >>> map(cube, range(1, 11))
- [1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]
- >>>
+ >>> def cube(x): return x*x*x
+ ...
+ >>> map(cube, range(1, 11))
+ [1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]
+ >>>
\end{verbatim}
More than one sequence may be passed; the function must then have as
@@ -1389,12 +1389,12 @@
of lists into a list of pairs. For example:
\begin{verbatim}
- >>> seq = range(8)
- >>> def square(x): return x*x
- ...
- >>> map(None, seq, map(square, seq))
- [(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25), (6, 36), (7, 49)]
- >>>
+ >>> seq = range(8)
+ >>> def square(x): return x*x
+ ...
+ >>> map(None, seq, map(square, seq))
+ [(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25), (6, 36), (7, 49)]
+ >>>
\end{verbatim}
\verb\reduce(func, sequence)\ returns a single value constructed
@@ -1403,11 +1403,11 @@
example, to compute the sum of the numbers 1 through 10:
\begin{verbatim}
- >>> def add(x,y): return x+y
- ...
- >>> reduce(add, range(1, 11))
- 55
- >>>
+ >>> def add(x,y): return x+y
+ ...
+ >>> reduce(add, range(1, 11))
+ 55
+ >>>
\end{verbatim}
If there's only one item in the sequence, its value is returned; if
@@ -1419,21 +1419,21 @@
item, then to the result and the next item, and so on. For example,
\begin{verbatim}
- >>> def sum(seq):
- ... def add(x,y): return x+y
- ... return reduce(add, seq, 0)
- ...
- >>> sum(range(1, 11))
- 55
- >>> sum([])
- 0
- >>>
+ >>> def sum(seq):
+ ... def add(x,y): return x+y
+ ... return reduce(add, seq, 0)
+ ...
+ >>> sum(range(1, 11))
+ 55
+ >>> sum([])
+ 0
+ >>>
\end{verbatim}
-\section{The {\tt del} statement}
+\section{The \sectcode{del} statement}
There is a way to remove an item from a list given its index instead
-of its value: the {\tt del} statement. This can also be used to
+of its value: the \code{del} statement. This can also be used to
remove slices from a list (which we did earlier by assignment of an
empty list to the slice). For example:
@@ -1449,24 +1449,24 @@
>>>
\end{verbatim}\ecode
%
-{\tt del} can also be used to delete entire variables:
+\code{del} can also be used to delete entire variables:
\bcode\begin{verbatim}
>>> del a
>>>
\end{verbatim}\ecode
%
-Referencing the name {\tt a} hereafter is an error (at least until
-another value is assigned to it). We'll find other uses for {\tt del}
+Referencing the name \code{a} hereafter is an error (at least until
+another value is assigned to it). We'll find other uses for \code{del}
later.
\section{Tuples and Sequences}
We saw that lists and strings have many common properties, e.g.,
-indexing and slicing operations. They are two examples of {\em
-sequence} data types. Since Python is an evolving language, other
-sequence data types may be added. There is also another standard
-sequence data type: the {\em tuple}.
+indexing and slicing operations. They are two examples of
+\emph{sequence} data types. Since Python is an evolving language,
+other sequence data types may be added. There is also another
+standard sequence data type: the \emph{tuple}.
A tuple consists of a number of values separated by commas, for
instance:
@@ -1514,23 +1514,23 @@
>>>
\end{verbatim}\ecode
%
-The statement {\tt t = 12345, 54321, 'hello!'} is an example of {\em
-tuple packing}: the values {\tt 12345}, {\tt 54321} and {\tt 'hello!'}
-are packed together in a tuple. The reverse operation is also
-possible, e.g.:
+The statement \code{t = 12345, 54321, 'hello!'} is an example of
+\emph{tuple packing}: the values \code{12345}, \code{54321} and
+\code{'hello!'} are packed together in a tuple. The reverse operation
+is also possible, e.g.:
\bcode\begin{verbatim}
>>> x, y, z = t
>>>
\end{verbatim}\ecode
%
-This is called, appropriately enough, {\em tuple unpacking}. Tuple
+This is called, appropriately enough, \emph{tuple unpacking}. Tuple
unpacking requires that the list of variables on the left has the same
number of elements as the length of the tuple. Note that multiple
assignment is really just a combination of tuple packing and tuple
unpacking!
-Occasionally, the corresponding operation on lists is useful: {\em list
+Occasionally, the corresponding operation on lists is useful: \emph{list
unpacking}. This is supported by enclosing the list of variables in
square brackets:
@@ -1542,19 +1542,19 @@
\section{Dictionaries}
-Another useful data type built into Python is the {\em dictionary}.
+Another useful data type built into Python is the \emph{dictionary}.
Dictionaries are sometimes found in other languages as ``associative
memories'' or ``associative arrays''. Unlike sequences, which are
-indexed by a range of numbers, dictionaries are indexed by {\em keys},
+indexed by a range of numbers, dictionaries are indexed by \emph{keys},
which can be any non-mutable type; strings and numbers can always be
keys. Tuples can be used as keys if they contain only strings,
numbers, or tuples. You can't use lists as keys, since lists can be
modified in place using their \code{append()} method.
It is best to think of a dictionary as an unordered set of
-{\em key:value} pairs, with the requirement that the keys are unique
+\emph{key:value} pairs, with the requirement that the keys are unique
(within one dictionary).
-A pair of braces creates an empty dictionary: \verb/{}/.
+A pair of braces creates an empty dictionary: \code{\{\}}.
Placing a comma-separated list of key:value pairs within the
braces adds initial key:value pairs to the dictionary; this is also the
way dictionaries are written on output.
@@ -1562,15 +1562,15 @@
The main operations on a dictionary are storing a value with some key
and extracting the value given the key. It is also possible to delete
a key:value pair
-with {\tt del}.
+with \code{del}.
If you store using a key that is already in use, the old value
associated with that key is forgotten. It is an error to extract a
value using a non-existent key.
-The {\tt keys()} method of a dictionary object returns a list of all the
+The \code{keys()} method of a dictionary object returns a list of all the
keys used in the dictionary, in random order (if you want it sorted,
-just apply the {\tt sort()} method to the list of keys). To check
-whether a single key is in the dictionary, use the \verb/has_key()/
+just apply the \code{sort()} method to the list of keys). To check
+whether a single key is in the dictionary, use the \code{has_key()}
method of the dictionary.
Here is a small example using a dictionary:
@@ -1595,34 +1595,34 @@
\section{More on Conditions}
-The conditions used in {\tt while} and {\tt if} statements above can
+The conditions used in \code{while} and \code{if} statements above can
contain other operators besides comparisons.
-The comparison operators {\tt in} and {\tt not in} check whether a value
-occurs (does not occur) in a sequence. The operators {\tt is} and {\tt
-is not} compare whether two objects are really the same object; this
+The comparison operators \code{in} and \code{not in} check whether a value
+occurs (does not occur) in a sequence. The operators \code{is} and
+\code{is not} compare whether two objects are really the same object; this
only matters for mutable objects like lists. All comparison operators
have the same priority, which is lower than that of all numerical
operators.
-Comparisons can be chained: e.g., {\tt a < b == c} tests whether {\tt a}
-is less than {\tt b} and moreover {\tt b} equals {\tt c}.
+Comparisons can be chained: e.g., \code{a < b == c} tests whether \code{a}
+is less than \code{b} and moreover \code{b} equals \code{c}.
-Comparisons may be combined by the Boolean operators {\tt and} and {\tt
-or}, and the outcome of a comparison (or of any other Boolean
-expression) may be negated with {\tt not}. These all have lower
-priorities than comparison operators again; between them, {\tt not} has
-the highest priority, and {\tt or} the lowest, so that
-{\tt A and not B or C} is equivalent to {\tt (A and (not B)) or C}. Of
+Comparisons may be combined by the Boolean operators \code{and} and
+\code{or}, and the outcome of a comparison (or of any other Boolean
+expression) may be negated with \code{not}. These all have lower
+priorities than comparison operators again; between them, \code{not} has
+the highest priority, and \code{or} the lowest, so that
+\code{A and not B or C} is equivalent to \code{(A and (not B)) or C}. Of
course, parentheses can be used to express the desired composition.
-The Boolean operators {\tt and} and {\tt or} are so-called {\em
-shortcut} operators: their arguments are evaluated from left to right,
-and evaluation stops as soon as the outcome is determined. E.g., if
-{\tt A} and {\tt C} are true but {\tt B} is false, {\tt A and B and C}
-does not evaluate the expression C. In general, the return value of a
-shortcut operator, when used as a general value and not as a Boolean, is
-the last evaluated argument.
+The Boolean operators \code{and} and \code{or} are so-called
+\emph{shortcut} operators: their arguments are evaluated from left to
+right, and evaluation stops as soon as the outcome is determined.
+E.g., if \code{A} and \code{C} are true but \code{B} is false, \code{A
+and B and C} does not evaluate the expression C. In general, the
+return value of a shortcut operator, when used as a general value and
+not as a Boolean, is the last evaluated argument.
It is possible to assign the result of a comparison or other Boolean
expression to a variable. For example,
@@ -1640,7 +1640,7 @@
\section{Comparing Sequences and Other Types}
Sequence objects may be compared to other objects with the same
-sequence type. The comparison uses {\em lexicographical} ordering:
+sequence type. The comparison uses \emph{lexicographical} ordering:
first the first two items are compared, and if they differ this
determines the outcome of the comparison; if they are equal, the next
two items are compared, and so on, until either sequence is exhausted.
@@ -1681,24 +1681,24 @@
Therefore, if you want to write a somewhat longer program, you are
better off using a text editor to prepare the input for the interpreter
and running it with that file as input instead. This is known as creating a
-{\em script}. As your program gets longer, you may want to split it
+\emph{script}. As your program gets longer, you may want to split it
into several files for easier maintenance. You may also want to use a
handy function that you've written in several programs without copying
its definition into each program.
To support this, Python has a way to put definitions in a file and use
them in a script or in an interactive instance of the interpreter.
-Such a file is called a {\em module}; definitions from a module can be
-{\em imported} into other modules or into the {\em main} module (the
+Such a file is called a \emph{module}; definitions from a module can be
+\emph{imported} into other modules or into the \emph{main} module (the
collection of variables that you have access to in a script
executed at the top level
and in calculator mode).
A module is a file containing Python definitions and statements. The
-file name is the module name with the suffix {\tt .py} appended. Within
+file name is the module name with the suffix \file{.py} appended. Within
a module, the module's name (as a string) is available as the value of
-the global variable {\tt __name__}. For instance, use your favorite text
-editor to create a file called {\tt fibo.py} in the current directory
+the global variable \code{__name__}. For instance, use your favorite text
+editor to create a file called \file{fibo.py} in the current directory
with the following contents:
\bcode\begin{verbatim}
@@ -1707,15 +1707,15 @@
def fib(n): # write Fibonacci series up to n
a, b = 0, 1
while b < n:
- print b,
- a, b = b, a+b
+ print b,
+ a, b = b, a+b
def fib2(n): # return Fibonacci series up to n
result = []
a, b = 0, 1
while b < n:
- result.append(b)
- a, b = b, a+b
+ result.append(b)
+ a, b = b, a+b
return result
\end{verbatim}\ecode
%
@@ -1728,9 +1728,9 @@
\end{verbatim}\ecode
%
This does not enter the names of the functions defined in
-{\tt fibo}
+\code{fibo}
directly in the current symbol table; it only enters the module name
-{\tt fibo}
+\code{fibo}
there.
Using the module name you can access the functions:
@@ -1760,7 +1760,7 @@
definitions.
These statements are intended to initialize the module.
They are executed only the
-{\em first}
+\emph{first}
time the module is imported somewhere.%
\footnote{
In fact function definitions are also `statements' that are
@@ -1776,17 +1776,17 @@
On the other hand, if you know what you are doing you can touch a
module's global variables with the same notation used to refer to its
functions,
-{\tt modname.itemname}.
+\code{modname.itemname}.
Modules can import other modules.
It is customary but not required to place all
-{\tt import}
+\code{import}
statements at the beginning of a module (or script, for that matter).
The imported module names are placed in the importing module's global
symbol table.
There is a variant of the
-{\tt import}
+\code{import}
statement that imports names from a module directly into the importing
module's symbol table.
For example:
@@ -1799,7 +1799,7 @@
\end{verbatim}\ecode
%
This does not introduce the module name from which the imports are taken
-in the local symbol table (so in the example, {\tt fibo} is not
+in the local symbol table (so in the example, \code{fibo} is not
defined).
There is even a variant to import all names that a module defines:
@@ -1812,45 +1812,45 @@
\end{verbatim}\ecode
%
This imports all names except those beginning with an underscore
-({\tt _}).
+(\code{_}).
\subsection{The Module Search Path}
-When a module named {\tt spam} is imported, the interpreter searches
-for a file named {\tt spam.py} in the current directory,
+When a module named \code{spam} is imported, the interpreter searches
+for a file named \file{spam.py} in the current directory,
and then in the list of directories specified by
-the environment variable {\tt PYTHONPATH}. This has the same syntax as
-the \UNIX{} shell variable {\tt PATH}, i.e., a list of colon-separated
-directory names. When {\tt PYTHONPATH} is not set, or when the file
+the environment variable \code{PYTHONPATH}. This has the same syntax as
+the \UNIX{} shell variable \code{PATH}, i.e., a list of colon-separated
+directory names. When \code{PYTHONPATH} is not set, or when the file
is not found there, the search continues in an installation-dependent
-default path, usually {\tt .:/usr/local/lib/python}.
+default path, usually \code{.:/usr/local/lib/python}.
Actually, modules are searched in the list of directories given by the
-variable {\tt sys.path} which is initialized from the directory
-containing the input script (or the current directory), {\tt
-PYTHONPATH} and the installation-dependent default. This allows
+variable \code{sys.path} which is initialized from the directory
+containing the input script (or the current directory),
+\code{PYTHONPATH} and the installation-dependent default. This allows
Python programs that know what they're doing to modify or replace the
module search path. See the section on Standard Modules later.
\subsection{``Compiled'' Python files}
As an important speed-up of the start-up time for short programs that
-use a lot of standard modules, if a file called {\tt spam.pyc} exists
-in the directory where {\tt spam.py} is found, this is assumed to
-contain an already-``compiled'' version of the module {\tt spam}. The
-modification time of the version of {\tt spam.py} used to create {\tt
-spam.pyc} is recorded in {\tt spam.pyc}, and the file is ignored if
-these don't match.
+use a lot of standard modules, if a file called \file{spam.pyc} exists
+in the directory where \file{spam.py} is found, this is assumed to
+contain an already-``compiled'' version of the module \code{spam}. The
+modification time of the version of \file{spam.py} used to create
+\file{spam.pyc} is recorded in \file{spam.pyc}, and the file is
+ignored if these don't match.
-Normally, you don't need to do anything to create the {\tt spam.pyc} file.
-Whenever {\tt spam.py} is successfully compiled, an attempt is made to
-write the compiled version to {\tt spam.pyc}. It is not an error if
+Normally, you don't need to do anything to create the \file{spam.pyc} file.
+Whenever \file{spam.py} is successfully compiled, an attempt is made to
+write the compiled version to \file{spam.pyc}. It is not an error if
this attempt fails; if for any reason the file is not written
-completely, the resulting {\tt spam.pyc} file will be recognized as
-invalid and thus ignored later. The contents of the {\tt spam.pyc}
+completely, the resulting \file{spam.pyc} file will be recognized as
+invalid and thus ignored later. The contents of the \file{spam.pyc}
file is platform independent, so a Python module directory can be
shared by machines of different architectures. (Tip for experts:
-the module {\tt compileall} creates {\tt .pyc} files for all modules.)
+the module \code{compileall} creates file{.pyc} files for all modules.)
XXX Should optimization with -O be covered here?
@@ -1862,11 +1862,11 @@
core of the language but are nevertheless built in, either for
efficiency or to provide access to operating system primitives such as
system calls. The set of such modules is a configuration option; e.g.,
-the {\tt amoeba} module is only provided on systems that somehow support
-Amoeba primitives. One particular module deserves some attention: {\tt
-sys}, which is built into every Python interpreter. The variables {\tt
-sys.ps1} and {\tt sys.ps2} define the strings used as primary and
-secondary prompts:
+the \code{amoeba} module is only provided on systems that somehow support
+Amoeba primitives. One particular module deserves some attention:
+\code{sys}, which is built into every Python interpreter. The
+variables \code{sys.ps1} and \code{sys.ps2} define the strings used as
+primary and secondary prompts:
\bcode\begin{verbatim}
>>> import sys
@@ -1884,13 +1884,13 @@
interactive mode.
The variable
-{\tt sys.path}
+\code{sys.path}
is a list of strings that determine the interpreter's search path for
modules.
It is initialized to a default path taken from the environment variable
-{\tt PYTHONPATH},
+\code{PYTHONPATH},
or from a built-in default if
-{\tt PYTHONPATH}
+\code{PYTHONPATH}
is not set.
You can modify it using standard list operations, e.g.:
@@ -1900,9 +1900,9 @@
>>>
\end{verbatim}\ecode
-\section{The {\tt dir()} function}
+\section{The \sectcode{dir()} function}
-The built-in function {\tt dir} is used to find out which names a module
+The built-in function \code{dir()} is used to find out which names a module
defines. It returns a sorted list of strings:
\bcode\begin{verbatim}
@@ -1916,7 +1916,7 @@
>>>
\end{verbatim}\ecode
%
-Without arguments, {\tt dir()} lists the names you have defined currently:
+Without arguments, \code{dir()} lists the names you have defined currently:
\bcode\begin{verbatim}
>>> a = [1, 2, 3, 4, 5]
@@ -1929,9 +1929,9 @@
%
Note that it lists all types of names: variables, modules, functions, etc.
-{\tt dir()} does not list the names of built-in functions and variables.
+\code{dir()} does not list the names of built-in functions and variables.
If you want a list of those, they are defined in the standard module
-{\tt __builtin__}:
+\code{__builtin__}:
\bcode\begin{verbatim}
>>> import __builtin__
@@ -1956,28 +1956,28 @@
This chapter will discuss some of the possibilities.
\section{Fancier Output Formatting}
-So far we've encountered two ways of writing values: {\em expression
-statements} and the {\tt print} statement. (A third way is using the
-{\tt write} method of file objects; the standard output file can be
-referenced as {\tt sys.stdout}. See the Library Reference for more
+So far we've encountered two ways of writing values: \emph{expression
+statements} and the \code{print} statement. (A third way is using the
+\code{write} method of file objects; the standard output file can be
+referenced as \code{sys.stdout}. See the Library Reference for more
information on this.)
Often you'll want more control over the formatting of your output than
simply printing space-separated values. There are two ways to format
your output; the first way is to do all the string handling yourself;
using string slicing and concatenation operations you can create any
-lay-out you can imagine. The standard module {\tt string} contains
+lay-out you can imagine. The standard module \code{string} contains
some useful operations for padding strings to a given column width;
these will be discussed shortly. The second way is to use the
\code{\%} operator with a string as the left argument. \code{\%}
-interprets the left argument as a \C\ \code{sprintf()}-style format
+interprets the left argument as a \C{} \code{sprintf()}-style format
string to be applied to the right argument, and returns the string
resulting from this formatting operation.
One question remains, of course: how do you convert values to strings?
Luckily, Python has a way to convert any value to a string: pass it to
-the \verb/repr()/ function, or just write the value between reverse
-quotes (\verb/``/). Some examples:
+the \code{repr()} function, or just write the value between reverse
+quotes (\code{``}). Some examples:
\bcode\begin{verbatim}
>>> x = 10 * 3.14
@@ -2036,20 +2036,20 @@
>>>
\end{verbatim}\ecode
%
-(Note that one space between each column was added by the way {\tt print}
+(Note that one space between each column was added by the way \code{print}
works: it always adds spaces between its arguments.)
-This example demonstrates the function {\tt string.rjust()}, which
+This example demonstrates the function \code{string.rjust()}, which
right-justifies a string in a field of a given width by padding it with
-spaces on the left. There are similar functions {\tt string.ljust()}
-and {\tt string.center()}. These functions do not write anything, they
+spaces on the left. There are similar functions \code{string.ljust()}
+and \code{string.center()}. These functions do not write anything, they
just return a new string. If the input string is too long, they don't
truncate it, but return it unchanged; this will mess up your column
lay-out but that's usually better than the alternative, which would be
lying about a value. (If you really want truncation you can always add
-a slice operation, as in {\tt string.ljust(x,~n)[0:n]}.)
+a slice operation, as in \code{string.ljust(x,~n)[0:n]}.)
-There is another function, {\tt string.zfill}, which pads a numeric
+There is another function, \code{string.zfill()}, which pads a numeric
string on the left with zeros. It understands about plus and minus
signs:
@@ -2066,24 +2066,24 @@
Using the \code{\%} operator looks like this:
\begin{verbatim}
- >>> import math
- >>> print 'The value of PI is approximately %5.3f.' % math.pi
- The value of PI is approximately 3.142.
- >>>
+ >>> import math
+ >>> print 'The value of PI is approximately %5.3f.' % math.pi
+ The value of PI is approximately 3.142.
+ >>>
\end{verbatim}
If there is more than one format in the string you pass a tuple as
right operand, e.g.
\begin{verbatim}
- >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
- >>> for name, phone in table.items():
- ... print '%-10s ==> %10d' % (name, phone)
- ...
- Jack ==> 4098
- Dcab ==> 8637678
- Sjoerd ==> 4127
- >>>
+ >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
+ >>> for name, phone in table.items():
+ ... print '%-10s ==> %10d' % (name, phone)
+ ...
+ Jack ==> 4098
+ Dcab ==> 8637678
+ Sjoerd ==> 4127
+ >>>
\end{verbatim}
Most formats work exactly as in C and require that you pass the proper
@@ -2100,10 +2100,10 @@
an extension of C formats using the form \verb\%(name)format\, e.g.
\begin{verbatim}
- >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
- >>> print 'Jack: %(Jack)d; Sjoerd: %(Sjoerd)d; Dcab: %(Dcab)d' % table
- Jack: 4098; Sjoerd: 4127; Dcab: 8637678
- >>>
+ >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
+ >>> print 'Jack: %(Jack)d; Sjoerd: %(Sjoerd)d; Dcab: %(Dcab)d' % table
+ Jack: 4098; Sjoerd: 4127; Dcab: 8637678
+ >>>
\end{verbatim}
This is particularly useful in combination with the new built-in
@@ -2162,11 +2162,11 @@
\end{verbatim}\ecode
%
\code{f.readline()} reads a single line from the file; a newline
-character (\verb/\n/) is left at the end of the string, and is only
+character (\code{\\n}) is left at the end of the string, and is only
omitted on the last line of the file if the file doesn't end in a
newline. This makes the return value unambiguous; if
\code{f.readline()} returns an empty string, the end of the file has
-been reached, while a blank line is represented by \verb/'\n'/, a
+been reached, while a blank line is represented by \code{'\\n'}, a
string containing only a single newline.
\bcode\begin{verbatim}
@@ -2178,7 +2178,7 @@
''
\end{verbatim}\ecode
%
-\code{f.readlines()} uses {\code{f.readline()} repeatedly, and returns
+\code{f.readlines()} uses \code{f.readline()} repeatedly, and returns
a list containing all the lines of data in the file.
\bcode\begin{verbatim}
@@ -2284,8 +2284,8 @@
Until now error messages haven't been more than mentioned, but if you
have tried out the examples you have probably seen some. There are
-(at least) two distinguishable kinds of errors: {\em syntax\ errors}
-and {\em exceptions}.
+(at least) two distinguishable kinds of errors: \emph{syntax errors}
+and \emph{exceptions}.
\section{Syntax Errors}
@@ -2304,9 +2304,9 @@
The parser repeats the offending line and displays a little `arrow'
pointing at the earliest point in the line where the error was detected.
The error is caused by (or at least detected at) the token
-{\em preceding}
+\emph{preceding}
the arrow: in the example, the error is detected at the keyword
-{\tt print}, since a colon ({\tt :}) is missing before it.
+\code{print}, since a colon (\code{:}) is missing before it.
File name and line number are printed so you know where to look in case
the input came from a script.
@@ -2314,7 +2314,7 @@
Even if a statement or expression is syntactically correct, it may
cause an error when an attempt is made to execute it.
-Errors detected during execution are called {\em exceptions} and are
+Errors detected during execution are called \emph{exceptions} and are
not unconditionally fatal: you will soon learn how to handle them in
Python programs. Most exceptions are not handled by programs,
however, and result in error messages as shown here:
@@ -2338,10 +2338,10 @@
The last line of the error message indicates what happened.
Exceptions come in different types, and the type is printed as part of
the message: the types in the example are
-{\tt ZeroDivisionError},
-{\tt NameError}
+\code{ZeroDivisionError},
+\code{NameError}
and
-{\tt TypeError}.
+\code{TypeError}.
The string printed as the exception type is the name of the built-in
name for the exception that occurred. This is true for all built-in
exceptions, but need not be true for user-defined exceptions (although
@@ -2382,35 +2382,35 @@
>>>
\end{verbatim}\ecode
%
-The {\tt try} statement works as follows.
+The \code{try} statement works as follows.
\begin{itemize}
\item
First, the
-{\em try\ clause}
-(the statement(s) between the {\tt try} and {\tt except} keywords) is
+\emph{try\ clause}
+(the statement(s) between the \code{try} and \code{except} keywords) is
executed.
\item
If no exception occurs, the
-{\em except\ clause}
-is skipped and execution of the {\tt try} statement is finished.
+\emph{except\ clause}
+is skipped and execution of the \code{try} statement is finished.
\item
If an exception occurs during execution of the try clause,
the rest of the clause is skipped. Then if
-its type matches the exception named after the {\tt except} keyword,
+its type matches the exception named after the \code{except} keyword,
the rest of the try clause is skipped, the except clause is executed,
-and then execution continues after the {\tt try} statement.
+and then execution continues after the \code{try} statement.
\item
If an exception occurs which does not match the exception named in the
except clause, it is passed on to outer try statements; if no handler is
found, it is an
-{\em unhandled\ exception}
+\emph{unhandled exception}
and execution stops with a message as shown above.
\end{itemize}
-A {\tt try} statement may have more than one except clause, to specify
+A \code{try} statement may have more than one except clause, to specify
handlers for different exceptions.
At most one handler will be executed.
Handlers only handle exceptions that occur in the corresponding try
-clause, not in other handlers of the same {\tt try} statement.
+clause, not in other handlers of the same \code{try} statement.
An except clause may name multiple exceptions as a parenthesized list,
e.g.:
@@ -2430,20 +2430,20 @@
exception. For example:
\begin{verbatim}
- for arg in sys.argv:
- try:
- f = open(arg, 'r')
- except IOError:
- print 'cannot open', arg
- else:
- print arg, 'has', len(f.readlines()), 'lines'
- f.close()
+ for arg in sys.argv:
+ try:
+ f = open(arg, 'r')
+ except IOError:
+ print 'cannot open', arg
+ else:
+ print arg, 'has', len(f.readlines()), 'lines'
+ f.close()
\end{verbatim}
When an exception occurs, it may have an associated value, also known as
the exceptions's
-{\em argument}.
+\emph{argument}.
The presence and type of the argument depend on the exception type.
For exception types which have an argument, the except clause may
specify a variable after the exception name (or list) to receive the
@@ -2483,7 +2483,7 @@
\section{Raising Exceptions}
-The {\tt raise} statement allows the programmer to force a specified
+The \code{raise} statement allows the programmer to force a specified
exception to occur.
For example:
@@ -2495,7 +2495,7 @@
>>>
\end{verbatim}\ecode
%
-The first argument to {\tt raise} names the exception to be raised.
+The first argument to \code{raise} names the exception to be raised.
The optional second argument specifies the exception's argument.
%
@@ -2528,7 +2528,7 @@
\section{Defining Clean-up Actions}
-The {\tt try} statement has another optional clause which is intended to
+The \code{try} statement has another optional clause which is intended to
define clean-up actions that must be executed under all circumstances.
For example:
@@ -2545,15 +2545,15 @@
>>>
\end{verbatim}\ecode
%
-A {\tt finally} clause is executed whether or not an exception has
-occurred in the {\tt try} clause. When an exception has occurred, it
-is re-raised after the {\tt finally} clause is executed. The
-{\tt finally} clause is also executed ``on the way out'' when the
-{\tt try} statement is left via a {\tt break} or {\tt return}
+A \code{finally} clause is executed whether or not an exception has
+occurred in the \code{try} clause. When an exception has occurred, it
+is re-raised after the \code{finally} clause is executed. The
+\code{finally} clause is also executed ``on the way out'' when the
+\code{try} statement is left via a \code{break} or \code{return}
statement.
-A {\tt try} statement must either have one or more {\tt except}
-clauses or one {\tt finally} clause, but not both.
+A \code{try} statement must either have one or more \code{except}
+clauses or one \code{finally} clause, but not both.
\chapter{Classes}
@@ -2569,7 +2569,7 @@
same name. Objects can contain an arbitrary amount of private data.
In \Cpp{} terminology, all class members (including the data members) are
-{\em public}, and all member functions are {\em virtual}. There are
+\emph{public}, and all member functions are \emph{virtual}. There are
no special constructors or destructors. As in Modula-3, there are no
shorthands for referencing the object's members from its methods: the
method function is declared with an explicit first argument
@@ -2594,7 +2594,7 @@
necessarily mean a class instance. Like \Cpp{} and Modula-3, and unlike
Smalltalk, not all types in Python are classes: the basic built-in
types like integers and lists aren't, and even somewhat more exotic
-types like files aren't. However, {\em all} Python types share a little
+types like files aren't. However, \emph{all} Python types share a little
bit of common semantics that is best described by using the word
object.
@@ -2624,7 +2624,7 @@
Let's begin with some definitions.
-A {\em name space} is a mapping from names to objects. Most name
+A \emph{name space} is a mapping from names to objects. Most name
spaces are currently implemented as Python dictionaries, but that's
normally not noticeable in any way (except for performance), and it
may change in the future. Examples of name spaces are: the set of
@@ -2637,7 +2637,7 @@
define a function ``maximize'' without confusion --- users of the
modules must prefix it with the module name.
-By the way, I use the word {\em attribute} for any name following a
+By the way, I use the word \emph{attribute} for any name following a
dot --- for example, in the expression \verb\z.real\, \verb\real\ is
an attribute of the object \verb\z\. Strictly speaking, references to
names in modules are attribute references: in the expression
@@ -2647,9 +2647,9 @@
global names defined in the module: they share the same name space!%
\footnote{
Except for one thing. Module objects have a secret read-only
- attribute called {\tt __dict__} which returns the dictionary
+ attribute called \code{__dict__} which returns the dictionary
used to implement the module's name space; the name
- {\tt __dict__} is an attribute but not a global name.
+ \code{__dict__} is an attribute but not a global name.
Obviously, using this violates the abstraction of name space
implementation, and should be restricted to things like
post-mortem debuggers...
@@ -2678,7 +2678,7 @@
be a better way to describe what actually happens.) Of course,
recursive invocations each have their own local name space.
-A {\em scope} is a textual region of a Python program where a name space
+A \emph{scope} is a textual region of a Python program where a name space
is directly accessible. ``Directly accessible'' here means that an
unqualified reference to a name attempts to find the name in the name
space.
@@ -2727,12 +2727,12 @@
The simplest form of class definition looks like this:
\begin{verbatim}
- class ClassName:
- <statement-1>
- .
- .
- .
- <statement-N>
+ class ClassName:
+ <statement-1>
+ .
+ .
+ .
+ <statement-N>
\end{verbatim}
Class definitions, like function definitions (\verb\def\ statements)
@@ -2752,7 +2752,7 @@
go into this new name space. In particular, function definitions bind
the name of the new function here.
-When a class definition is left normally (via the end), a {\em class
+When a class definition is left normally (via the end), a \emph{class
object} is created. This is basically a wrapper around the contents
of the name space created by the class definition; we'll learn more
about class objects in the next section. The original local scope
@@ -2766,18 +2766,18 @@
Class objects support two kinds of operations: attribute references
and instantiation.
-{\em Attribute references} use the standard syntax used for all
+\emph{Attribute references} use the standard syntax used for all
attribute references in Python: \verb\obj.name\. Valid attribute
names are all the names that were in the class's name space when the
class object was created. So, if the class definition looked like
this:
\begin{verbatim}
- class MyClass:
- "A simple example class"
- i = 12345
- def f(x):
- return 'hello world'
+ class MyClass:
+ "A simple example class"
+ i = 12345
+ def f(x):
+ return 'hello world'
\end{verbatim}
then \verb\MyClass.i\ and \verb\MyClass.f\ are valid attribute
@@ -2787,16 +2787,16 @@
attribute that's read-only, returning the docstring belonging to
the class: \verb\"A simple example class"\).
-Class {\em instantiation} uses function notation. Just pretend that
+Class \emph{instantiation} uses function notation. Just pretend that
the class object is a parameterless function that returns a new
instance of the class. For example, (assuming the above class):
\begin{verbatim}
- x = MyClass()
+ x = MyClass()
\end{verbatim}
-creates a new {\em instance} of the class and assigns this object to
-the local variable \verb\x\.
+creates a new \emph{instance} of the class and assigns this object to
+the local variable \code{x}.
\subsection{Instance objects}
@@ -2805,7 +2805,7 @@
understood by instance objects are attribute references. There are
two kinds of valid attribute names.
-The first I'll call {\em data attributes}. These correspond to
+The first I'll call \emph{data attributes}. These correspond to
``instance variables'' in Smalltalk, and to ``data members'' in \Cpp{}.
Data attributes need not be declared; like local variables, they
spring into existence when they are first assigned to. For example,
@@ -2814,15 +2814,15 @@
trace:
\begin{verbatim}
- x.counter = 1
- while x.counter < 10:
- x.counter = x.counter * 2
- print x.counter
- del x.counter
+ x.counter = 1
+ while x.counter < 10:
+ x.counter = x.counter * 2
+ print x.counter
+ del x.counter
\end{verbatim}
The second kind of attribute references understood by instance objects
-are {\em methods}. A method is a function that ``belongs to'' an
+are \emph{methods}. A method is a function that ``belongs to'' an
object. (In Python, the term method is not unique to class instances:
other object types can have methods as well, e.g., list objects have
methods called append, insert, remove, sort, and so on. However,
@@ -2832,10 +2832,10 @@
Valid method names of an instance object depend on its class. By
definition, all attributes of a class that are (user-defined) function
objects define corresponding methods of its instances. So in our
-example, \verb\x.f\ is a valid method reference, since
-\verb\MyClass.f\ is a function, but \verb\x.i\ is not, since
-\verb\MyClass.i\ is not. But \verb\x.f\ is not the
-same thing as \verb\MyClass.f\ --- it is a {\em method object}, not a
+example, \code{x.f} is a valid method reference, since
+\code{MyClass.f} is a function, but \code{x.i} is not, since
+\code{MyClass.i} is not. But \code{x.f} is not the
+same thing as \verb\MyClass.f\ --- it is a \emph{method object}, not a
function object.
@@ -2844,7 +2844,7 @@
Usually, a method is called immediately, e.g.:
\begin{verbatim}
- x.f()
+ x.f()
\end{verbatim}
In our example, this will return the string \verb\'hello world'\.
@@ -2853,9 +2853,9 @@
moment, for example:
\begin{verbatim}
- xf = x.f
- while 1:
- print xf()
+ xf = x.f
+ while 1:
+ print xf()
\end{verbatim}
will continue to print \verb\hello world\ until the end of time.
@@ -2871,7 +2871,7 @@
methods is that the object is passed as the first argument of the
function. In our example, the call \verb\x.f()\ is exactly equivalent
to \verb\MyClass.f(x)\. In general, calling a method with a list of
-{\em n} arguments is equivalent to calling the corresponding function
+\var{n} arguments is equivalent to calling the corresponding function
with an argument list that is created by inserting the method's object
before the first argument.
@@ -2930,7 +2930,7 @@
\verb\self\ has absolutely no special meaning to Python. (Note,
however, that by not following the convention your code may be less
readable by other Python programmers, and it is also conceivable that
-a {\em class browser} program be written which relies upon such a
+a \emph{class browser} program be written which relies upon such a
convention.)
@@ -2941,15 +2941,15 @@
example:
\begin{verbatim}
- # Function defined outside the class
- def f1(self, x, y):
- return min(x, x+y)
-
- class C:
- f = f1
- def g(self):
- return 'hello world'
- h = g
+ # Function defined outside the class
+ def f1(self, x, y):
+ return min(x, x+y)
+
+ class C:
+ f = f1
+ def g(self):
+ return 'hello world'
+ h = g
\end{verbatim}
Now \verb\f\, \verb\g\ and \verb\h\ are all attributes of class
@@ -2963,34 +2963,34 @@
\verb\self\ argument, e.g.:
\begin{verbatim}
- class Bag:
- def empty(self):
- self.data = []
- def add(self, x):
- self.data.append(x)
- def addtwice(self, x):
- self.add(x)
- self.add(x)
+ class Bag:
+ def empty(self):
+ self.data = []
+ def add(self, x):
+ self.data.append(x)
+ def addtwice(self, x):
+ self.add(x)
+ self.add(x)
\end{verbatim}
The instantiation operation (``calling'' a class object) creates an
empty object. Many classes like to create objects in a known initial
state. Therefore a class may define a special method named
-\verb\__init__\, like this:
+\code{__init__()}, like this:
\begin{verbatim}
- def __init__(self):
- self.empty()
+ def __init__(self):
+ self.empty()
\end{verbatim}
-When a class defines an \verb\__init__\ method, class instantiation
-automatically invokes \verb\__init__\ for the newly-created class
-instance. So in the \verb\Bag\ example, a new and initialized instance
+When a class defines an \code{__init__()} method, class instantiation
+automatically invokes \code{__init__()} for the newly-created class
+instance. So in the \code{Bag} example, a new and initialized instance
can be obtained by:
\begin{verbatim}
- x = Bag()
+ x = Bag()
\end{verbatim}
Of course, the \verb\__init__\ method may have arguments for greater
@@ -3028,12 +3028,12 @@
definition looks as follows:
\begin{verbatim}
- class DerivedClassName(BaseClassName):
- <statement-1>
- .
- .
- .
- <statement-N>
+ class DerivedClassName(BaseClassName):
+ <statement-1>
+ .
+ .
+ .
+ <statement-N>
\end{verbatim}
The name \verb\BaseClassName\ must be defined in a scope containing
@@ -3042,7 +3042,7 @@
defined in another module, e.g.,
\begin{verbatim}
- class DerivedClassName(modname.BaseClassName):
+ class DerivedClassName(modname.BaseClassName):
\end{verbatim}
Execution of a derived class definition proceeds the same as for a
@@ -3079,12 +3079,12 @@
class definition with multiple base classes looks as follows:
\begin{verbatim}
- class DerivedClassName(Base1, Base2, Base3):
- <statement-1>
- .
- .
- .
- <statement-N>
+ class DerivedClassName(Base1, Base2, Base3):
+ <statement-1>
+ .
+ .
+ .
+ <statement-N>
\end{verbatim}
The only rule necessary to explain the semantics is the resolution
@@ -3123,7 +3123,7 @@
is done without regard of the syntactic position of the identifier, so
it can be used to define class-private instance and class variables,
methods, as well as globals, and even to store instance variables
-private to this class on instances of {\em other} classes. Truncation
+private to this class on instances of \emph{other} classes. Truncation
may occur when the mangled name would be longer than 255 characters.
Outside classes, or when the class name consists of only underscores,
no mangling occurs.
@@ -3189,15 +3189,15 @@
items. An empty class definition will do nicely, e.g.:
\begin{verbatim}
- class Employee:
- pass
+ class Employee:
+ pass
- john = Employee() # Create an empty employee record
+ john = Employee() # Create an empty employee record
- # Fill the fields of the record
- john.name = 'John Doe'
- john.dept = 'computer lab'
- john.salary = 1000
+ # Fill the fields of the record
+ john.name = 'John Doe'
+ john.dept = 'computer lab'
+ john.salary = 1000
\end{verbatim}
@@ -3339,8 +3339,8 @@
overcome through the judicious use of default argument values, e.g.
\begin{verbatim}
- def make_incrementor(n):
- return lambda x, incr=n: x+incr
+ def make_incrementor(n):
+ return lambda x, incr=n: x+incr
\end{verbatim}
\section{Documentation Strings}
@@ -3368,7 +3368,7 @@
The Python parser does not strip indentation from multi-line string
literals in Python, so tools that process documentation have to strip
indentation. This is done using the following convention. The first
-non-blank line {\em after} the first line of the string determines the
+non-blank line \emph{after} the first line of the string determines the
amount of indentation for the entire documentation string. (We can't
use the first line since it is generally adjacent to the string's
opening quotes so its indentation is not apparent in the string
@@ -3384,7 +3384,7 @@
Some versions of the Python interpreter support editing of the current
input line and history substitution, similar to facilities found in
the Korn shell and the GNU Bash shell. This is implemented using the
-{\em GNU\ Readline} library, which supports Emacs-style and vi-style
+\emph{GNU Readline} library, which supports Emacs-style and vi-style
editing. This library has its own documentation which I won't
duplicate here; however, the basics are easily explained.
@@ -3416,7 +3416,7 @@
The key bindings and some other parameters of the Readline library can
be customized by placing commands in an initialization file called
-{\tt \$HOME/.inputrc}. Key bindings have the form
+\file{\$HOME/.inputrc}. Key bindings have the form
\bcode\begin{verbatim}
key-name: function-name
@@ -3455,7 +3455,7 @@
TAB: complete
\end{verbatim}\ecode
%
-in your {\tt \$HOME/.inputrc}. (Of course, this makes it hard to type
+in your \file{\$HOME/.inputrc}. (Of course, this makes it hard to type
indented continuation lines...)
\subsection{Commentary}
diff --git a/Doc/tut/tut.tex b/Doc/tut/tut.tex
index 0afcb3f..a3d8da8 100644
--- a/Doc/tut/tut.tex
+++ b/Doc/tut/tut.tex
@@ -42,8 +42,8 @@
Python interpreter handy for hands-on experience, but as the examples
are self-contained, the tutorial can be read off-line as well.
-For a description of standard objects and modules, see the {\em Python
-Library Reference} document. The {\em Python Reference Manual} gives
+For a description of standard objects and modules, see the \emph{Python
+Library Reference} document. The \emph{Python Reference Manual} gives
a more formal definition of the language.
\end{abstract}
@@ -104,12 +104,12 @@
simple to use, but it is a real programming language, offering much
more structure and support for large programs than the shell has. On
the other hand, it also offers much more error checking than C, and,
-being a {\em very-high-level language}, it has high-level data types
+being a \emph{very-high-level language}, it has high-level data types
built in, such as flexible arrays and dictionaries that would cost you
days to implement efficiently in C. Because of its more general data
-types Python is applicable to a much larger problem domain than {\em
-Awk} or even {\em Perl}, yet many things are at least as easy in
-Python as in those languages.
+types Python is applicable to a much larger problem domain than
+\emph{Awk} or even \emph{Perl}, yet many things are at least as easy
+in Python as in those languages.
Python allows you to split up your program in modules that can be
reused in other Python programs. It comes with a large collection of
@@ -139,7 +139,7 @@
no variable or argument declarations are necessary.
\end{itemize}
-Python is {\em extensible}: if you know how to program in C it is easy
+Python is \emph{extensible}: if you know how to program in C it is easy
to add a new built-in function or module to the interpreter, either to
perform critical operations at maximum speed, or to link Python
programs to libraries that may only be available in binary form (such
@@ -172,8 +172,8 @@
\section{Invoking the Interpreter}
-The Python interpreter is usually installed as {\tt /usr/local/bin/python}
-on those machines where it is available; putting {\tt /usr/local/bin} in
+The Python interpreter is usually installed as \file{/usr/local/bin/python}
+on those machines where it is available; putting \file{/usr/local/bin} in
your \UNIX{} shell's search path makes it possible to start it by
typing the command
@@ -183,8 +183,8 @@
%
to the shell. Since the choice of the directory where the interpreter
lives is an installation option, other places are possible; check with
-your local Python guru or system administrator. (E.g., {\tt
-/usr/local/python} is a popular alternative location.)
+your local Python guru or system administrator. (E.g.,
+\file{/usr/local/python} is a popular alternative location.)
Typing an EOF character (Control-D on \UNIX{}, Control-Z or F6 on DOS
or Windows) at the primary prompt causes the interpreter to exit with
@@ -199,27 +199,27 @@
quickest check to see whether command line editing is supported is
typing Control-P to the first Python prompt you get. If it beeps, you
have command line editing; see Appendix A for an introduction to the
-keys. If nothing appears to happen, or if \verb/^P/ is echoed,
+keys. If nothing appears to happen, or if \code{\^P} is echoed,
command line editing isn't available; you'll only be able to use
backspace to remove characters from the current line.
The interpreter operates somewhat like the \UNIX{} shell: when called
with standard input connected to a tty device, it reads and executes
commands interactively; when called with a file name argument or with
-a file as standard input, it reads and executes a {\em script} from
+a file as standard input, it reads and executes a \emph{script} from
that file.
A third way of starting the interpreter is
-``{\tt python -c command [arg] ...}'', which
-executes the statement(s) in {\tt command}, analogous to the shell's
-{\tt -c} option. Since Python statements often contain spaces or other
-characters that are special to the shell, it is best to quote {\tt
-command} in its entirety with double quotes.
+\samp{python -c command [arg] ...}, which
+executes the statement(s) in \code{command}, analogous to the shell's
+\code{-c} option. Since Python statements often contain spaces or other
+characters that are special to the shell, it is best to quote
+\code{command} in its entirety with double quotes.
-Note that there is a difference between ``{\tt python file}'' and
-``{\tt python <file}''. In the latter case, input requests from the
-program, such as calls to {\tt input()} and {\tt raw_input()}, are
-satisfied from {\em file}. Since this file has already been read
+Note that there is a difference between \samp{python file} and
+\samp{python <file}. In the latter case, input requests from the
+program, such as calls to \code{input()} and \code{raw_input()}, are
+satisfied from \emph{file}. Since this file has already been read
until the end by the parser before the program starts executing, the
program will encounter EOF immediately. In the former case (which is
usually what you want) they are satisfied from whatever file or device
@@ -227,39 +227,39 @@
When a script file is used, it is sometimes useful to be able to run
the script and enter interactive mode afterwards. This can be done by
-passing {\tt -i} before the script. (This does not work if the script
+passing \code{-i} before the script. (This does not work if the script
is read from standard input, for the same reason as explained in the
previous paragraph.)
\subsection{Argument Passing}
When known to the interpreter, the script name and additional
-arguments thereafter are passed to the script in the variable {\tt
-sys.argv}, which is a list of strings. Its length is at least one;
-when no script and no arguments are given, {\tt sys.argv[0]} is an
-empty string. When the script name is given as {\tt '-'} (meaning
-standard input), {\tt sys.argv[0]} is set to {\tt '-'}. When {\tt -c
-command} is used, {\tt sys.argv[0]} is set to {\tt '-c'}. Options
-found after {\tt -c command} are not consumed by the Python
-interpreter's option processing but left in {\tt sys.argv} for the
+arguments thereafter are passed to the script in the variable
+\code{sys.argv}, which is a list of strings. Its length is at least
+one; when no script and no arguments are given, \code{sys.argv[0]} is
+an empty string. When the script name is given as \code{'-'} (meaning
+standard input), \code{sys.argv[0]} is set to \code{'-'}. When \code{-c
+command} is used, \code{sys.argv[0]} is set to \code{'-c'}. Options
+found after \code{-c command} are not consumed by the Python
+interpreter's option processing but left in \code{sys.argv} for the
command to handle.
\subsection{Interactive Mode}
When commands are read from a tty, the interpreter is said to be in
-{\em interactive\ mode}. In this mode it prompts for the next command
-with the {\em primary\ prompt}, usually three greater-than signs ({\tt
->>>}); for continuation lines it prompts with the
-{\em secondary\ prompt},
-by default three dots ({\tt ...}).
+\emph{interactive mode}. In this mode it prompts for the next command
+with the \emph{primary prompt}, usually three greater-than signs
+(\code{>>>}); for continuation lines it prompts with the
+\emph{secondary prompt},
+by default three dots (\code{...}).
The interpreter prints a welcome message stating its version number
and a copyright notice before printing the first prompt, e.g.:
\bcode\begin{verbatim}
python
-Python 1.4 (Oct 25 1996) [GCC 2.7.2]
-Copyright 1991-1996 Stichting Mathematisch Centrum, Amsterdam
+Python 1.5b1 (#1, Dec 3 1997, 00:02:06) [GCC 2.7.2.2] on sunos5
+Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
>>>
\end{verbatim}\ecode
@@ -271,8 +271,8 @@
message and a stack trace. In interactive mode, it then returns to
the primary prompt; when input came from a file, it exits with a
nonzero exit status after printing
-the stack trace. (Exceptions handled by an {\tt except} clause in a
-{\tt try} statement are not errors in this context.) Some errors are
+the stack trace. (Exceptions handled by an \code{except} clause in a
+\code{try} statement are not errors in this context.) Some errors are
unconditionally fatal and cause an exit with a nonzero exit; this
applies to internal inconsistencies and some cases of running out of
memory. All error messages are written to the standard error stream;
@@ -285,9 +285,9 @@
\footnote{
A problem with the GNU Readline package may prevent this.
}
-Typing an interrupt while a command is executing raises the {\tt
-KeyboardInterrupt} exception, which may be handled by a {\tt try}
-statement.
+Typing an interrupt while a command is executing raises the
+\code{KeyboardInterrupt} exception, which may be handled by a
+\code{try} statement.
\subsection{Executable Python scripts}
@@ -299,7 +299,7 @@
\end{verbatim}\ecode
%
(assuming that the interpreter is on the user's PATH) at the beginning
-of the script and giving the file an executable mode. The {\tt \#!}
+of the script and giving the file an executable mode. The \code{\#!}
must be the first two characters of the file.
\subsection{The Interactive Startup File}
@@ -309,30 +309,30 @@
When you use Python interactively, it is frequently handy to have some
standard commands executed every time the interpreter is started. You
-can do this by setting an environment variable named {\tt
-PYTHONSTARTUP} to the name of a file containing your start-up
-commands. This is similar to the {\tt .profile} feature of the \UNIX{}
+can do this by setting an environment variable named
+\code{PYTHONSTARTUP} to the name of a file containing your start-up
+commands. This is similar to the \file{.profile} feature of the \UNIX{}
shells.
This file is only read in interactive sessions, not when Python reads
-commands from a script, and not when {\tt /dev/tty} is given as the
+commands from a script, and not when \file{/dev/tty} is given as the
explicit source of commands (which otherwise behaves like an
interactive session). It is executed in the same name space where
interactive commands are executed, so that objects that it defines or
imports can be used without qualification in the interactive session.
-You can also change the prompts {\tt sys.ps1} and {\tt sys.ps2} in
+You can also change the prompts \code{sys.ps1} and \code{sys.ps2} in
this file.
If you want to read an additional start-up file from the current
directory, you can program this in the global start-up file, e.g.
-\verb\execfile('.pythonrc')\. If you want to use the startup file
+\code{execfile('.pythonrc')}. If you want to use the startup file
in a script, you must write this explicitly in the script, e.g.
-\verb\import os;\ \verb\execfile(os.environ['PYTHONSTARTUP'])\.
+\code{import os;} \code{execfile(os.environ['PYTHONSTARTUP'])}.
\chapter{An Informal Introduction to Python}
In the following examples, input and output are distinguished by the
-presence or absence of prompts ({\tt >>>} and {\tt ...}): to repeat
+presence or absence of prompts (\code{>>>} and \code{...}): to repeat
the example, you must type everything after the prompt, when the
prompt appears; lines that do not begin with a prompt are output from
the interpreter.%
@@ -347,13 +347,13 @@
\section{Using Python as a Calculator}
Let's try some simple Python commands. Start the interpreter and wait
-for the primary prompt, {\tt >>>}. (It shouldn't take long.)
+for the primary prompt, \code{>>>}. (It shouldn't take long.)
\subsection{Numbers}
The interpreter acts as a simple calculator: you can type an
expression at it and it will write the value. Expression syntax is
-straightforward: the operators {\tt +}, {\tt -}, {\tt *} and {\tt /}
+straightforward: the operators \code{+}, \code{-}, \code{*} and \code{/}
work just like in most other languages (e.g., Pascal or C); parentheses
can be used for grouping. For example:
@@ -375,7 +375,7 @@
>>>
\end{verbatim}\ecode
%
-Like in C, the equal sign ({\tt =}) is used to assign a value to a
+Like in C, the equal sign (\code{=}) is used to assign a value to a
variable. The value of an assignment is not written:
\bcode\begin{verbatim}
@@ -542,11 +542,11 @@
funny characters escaped by backslashes, to show the precise
value. The string is enclosed in double quotes if the string contains
a single quote and no double quotes, else it's enclosed in single
-quotes. (The {\tt print} statement, described later, can be used to
+quotes. (The \code{print} statement, described later, can be used to
write strings without quotes or escapes.)
-Strings can be concatenated (glued together) with the {\tt +}
-operator, and repeated with {\tt *}:
+Strings can be concatenated (glued together) with the \code{+}
+operator, and repeated with \code{*}:
\bcode\begin{verbatim}
>>> word = 'Help' + 'A'
@@ -564,7 +564,7 @@
Strings can be subscripted (indexed); like in C, the first character
of a string has subscript (index) 0. There is no separate character
type; a character is simply a string of size one. Like in Icon,
-substrings can be specified with the {\em slice} notation: two indices
+substrings can be specified with the \emph{slice} notation: two indices
separated by a colon.
\bcode\begin{verbatim}
@@ -589,8 +589,8 @@
>>>
\end{verbatim}\ecode
%
-Here's a useful invariant of slice operations: \verb\s[:i] + s[i:]\
-equals \verb\s\.
+Here's a useful invariant of slice operations: \code{s[:i] + s[i:]}
+equals \code{s}.
\bcode\begin{verbatim}
>>> word[:2] + word[2:]
@@ -652,9 +652,9 @@
\end{verbatim}\ecode
%
The best way to remember how slices work is to think of the indices as
-pointing {\em between} characters, with the left edge of the first
+pointing \emph{between} characters, with the left edge of the first
character numbered 0. Then the right edge of the last character of a
-string of {\tt n} characters has index {\tt n}, for example:
+string of \var{n} characters has index \var{n}, for example:
\bcode\begin{verbatim}
+---+---+---+---+---+
@@ -666,14 +666,14 @@
%
The first row of numbers gives the position of the indices 0...5 in
the string; the second row gives the corresponding negative indices.
-The slice from \verb\i\ to \verb\j\ consists of all characters between
-the edges labeled \verb\i\ and \verb\j\, respectively.
+The slice from \var{i} to \var{j} consists of all characters between
+the edges labeled \var{i} and \var{j}, respectively.
For nonnegative indices, the length of a slice is the difference of
the indices, if both are within bounds, e.g., the length of
-\verb\word[1:3]\ is 2.
+\code{word[1:3]} is 2.
-The built-in function {\tt len()} returns the length of a string:
+The built-in function \code{len()} returns the length of a string:
\bcode\begin{verbatim}
>>> s = 'supercalifragilisticexpialidocious'
@@ -684,8 +684,8 @@
\subsection{Lists}
-Python knows a number of {\em compound} data types, used to group
-together other values. The most versatile is the {\em list}, which
+Python knows a number of \emph{compound} data types, used to group
+together other values. The most versatile is the \emph{list}, which
can be written as a list of comma-separated values (items) between
square brackets. List items need not all have the same type.
@@ -715,7 +715,7 @@
>>>
\end{verbatim}\ecode
%
-Unlike strings, which are {\em immutable}, it is possible to change
+Unlike strings, which are \emph{immutable}, it is possible to change
individual elements of a list:
\bcode\begin{verbatim}
@@ -749,7 +749,7 @@
>>>
\end{verbatim}\ecode
%
-The built-in function {\tt len()} also applies to lists:
+The built-in function \code{len()} also applies to lists:
\bcode\begin{verbatim}
>>> len(a)
@@ -777,14 +777,14 @@
>>>
\end{verbatim}\ecode
%
-Note that in the last example, {\tt p[1]} and {\tt q} really refer to
-the same object! We'll come back to {\em object semantics} later.
+Note that in the last example, \code{p[1]} and \code{q} really refer to
+the same object! We'll come back to \emph{object semantics} later.
\section{First Steps Towards Programming}
Of course, we can use Python for more complicated tasks than adding
two and two together. For instance, we can write an initial
-subsequence of the {\em Fibonacci} series as follows:
+subsequence of the \emph{Fibonacci} series as follows:
\bcode\begin{verbatim}
>>> # Fibonacci series:
@@ -808,23 +808,23 @@
\begin{itemize}
\item
-The first line contains a {\em multiple assignment}: the variables
-{\tt a} and {\tt b} simultaneously get the new values 0 and 1. On the
+The first line contains a \emph{multiple assignment}: the variables
+\code{a} and \code{b} simultaneously get the new values 0 and 1. On the
last line this is used again, demonstrating that the expressions on
the right-hand side are all evaluated first before any of the
assignments take place.
\item
-The {\tt while} loop executes as long as the condition (here: {\tt b <
+The \code{while} loop executes as long as the condition (here: \code{b <
10}) remains true. In Python, like in C, any non-zero integer value is
true; zero is false. The condition may also be a string or list value,
in fact any sequence; anything with a non-zero length is true, empty
sequences are false. The test used in the example is a simple
comparison. The standard comparison operators are written the same as
-in C: {\tt <}, {\tt >}, {\tt ==}, {\tt <=}, {\tt >=} and {\tt !=}.
+in C: \code{<}, \code{>}, \code{==}, \code{<=}, \code{>=} and \code{!=}.
\item
-The {\em body} of the loop is {\em indented}: indentation is Python's
+The \emph{body} of the loop is \emph{indented}: indentation is Python's
way of grouping statements. Python does not (yet!) provide an
intelligent input line editing facility, so you have to type a tab or
space(s) for each indented line. In practice you will prepare more
@@ -835,7 +835,7 @@
line).
\item
-The {\tt print} statement writes the value of the expression(s) it is
+The \code{print} statement writes the value of the expression(s) it is
given. It differs from just writing the expression you want to write
(as we did earlier in the calculator examples) in the way it handles
multiple expressions and strings. Strings are printed without quotes,
@@ -869,13 +869,13 @@
\chapter{More Control Flow Tools}
-Besides the {\tt while} statement just introduced, Python knows the
+Besides the \code{while} statement just introduced, Python knows the
usual control flow statements known from other languages, with some
twists.
\section{If Statements}
-Perhaps the most well-known statement type is the {\tt if} statement.
+Perhaps the most well-known statement type is the \code{if} statement.
For example:
\bcode\begin{verbatim}
@@ -891,20 +891,20 @@
...
\end{verbatim}\ecode
%
-There can be zero or more {\tt elif} parts, and the {\tt else} part is
-optional. The keyword `{\tt elif}' is short for `{\tt else if}', and is
-useful to avoid excessive indentation. An {\tt if...elif...elif...}
-sequence is a substitute for the {\em switch} or {\em case} statements
+There can be zero or more \code{elif} parts, and the \code{else} part is
+optional. The keyword `\code{elif}' is short for `\code{else if}', and is
+useful to avoid excessive indentation. An \code{if...elif...elif...}
+sequence is a substitute for the \emph{switch} or \emph{case} statements
found in other languages.
\section{For Statements}
-The {\tt for} statement in Python differs a bit from what you may be
+The \code{for} statement in Python differs a bit from what you may be
used to in C or Pascal. Rather than always iterating over an
arithmetic progression of numbers (like in Pascal), or leaving the user
-completely free in the iteration test and step (as C), Python's {\tt
-for} statement iterates over the items of any sequence (e.g., a list
-or a string), in the order that they appear in the sequence. For
+completely free in the iteration test and step (as C), Python's
+\code{for} statement iterates over the items of any sequence (e.g., a
+list or a string), in the order that they appear in the sequence. For
example (no pun intended):
\bcode\begin{verbatim}
@@ -934,10 +934,10 @@
>>>
\end{verbatim}\ecode
-\section{The {\tt range()} Function}
+\section{The \sectcode{range()} Function}
If you do need to iterate over a sequence of numbers, the built-in
-function {\tt range()} comes in handy. It generates lists containing
+function \code{range()} comes in handy. It generates lists containing
arithmetic progressions, e.g.:
\bcode\begin{verbatim}
@@ -946,7 +946,7 @@
>>>
\end{verbatim}\ecode
%
-The given end point is never part of the generated list; {\tt range(10)}
+The given end point is never part of the generated list; \code{range(10)}
generates a list of 10 values, exactly the legal indices for items of a
sequence of length 10. It is possible to let the range start at another
number, or to specify a different increment (even negative):
@@ -961,8 +961,8 @@
>>>
\end{verbatim}\ecode
%
-To iterate over the indices of a sequence, combine {\tt range()} and
-{\tt len()} as follows:
+To iterate over the indices of a sequence, combine \code{range()} and
+\code{len()} as follows:
\bcode\begin{verbatim}
>>> a = ['Mary', 'had', 'a', 'little', 'lamb']
@@ -979,16 +979,16 @@
\section{Break and Continue Statements, and Else Clauses on Loops}
-The {\tt break} statement, like in C, breaks out of the smallest
-enclosing {\tt for} or {\tt while} loop.
+The \code{break} statement, like in C, breaks out of the smallest
+enclosing \code{for} or \code{while} loop.
-The {\tt continue} statement, also borrowed from C, continues with the
+The \code{continue} statement, also borrowed from C, continues with the
next iteration of the loop.
-Loop statements may have an {\tt else} clause; it is executed when the
-loop terminates through exhaustion of the list (with {\tt for}) or when
-the condition becomes false (with {\tt while}), but not when the loop is
-terminated by a {\tt break} statement. This is exemplified by the
+Loop statements may have an \code{else} clause; it is executed when the
+loop terminates through exhaustion of the list (with \code{for}) or when
+the condition becomes false (with \code{while}), but not when the loop is
+terminated by a \code{break} statement. This is exemplified by the
following loop, which searches for prime numbers:
\bcode\begin{verbatim}
@@ -1013,7 +1013,7 @@
\section{Pass Statements}
-The {\tt pass} statement does nothing.
+The \code{pass} statement does nothing.
It can be used when a statement is required syntactically but the
program requires no action.
For example:
@@ -1034,8 +1034,8 @@
... "Print a Fibonacci series up to n"
... a, b = 0, 1
... while b < n:
-... print b,
-... a, b = b, a+b
+... print b,
+... a, b = b, a+b
...
>>> # Now call the function we just defined:
... fib(2000)
@@ -1043,7 +1043,7 @@
>>>
\end{verbatim}\ecode
%
-The keyword {\tt def} introduces a function {\em definition}. It must
+The keyword \code{def} introduces a function \emph{definition}. It must
be followed by the function name and the parenthesized list of formal
parameters. The statements that form the body of the function start
at the next line, indented by a tab stop. The first statement of the
@@ -1054,21 +1054,21 @@
it's good practice to include docstrings in code that you write, so
try to make a habit of it.
-The {\em execution} of a function introduces a new symbol table used
+The \emph{execution} of a function introduces a new symbol table used
for the local variables of the function. More precisely, all variable
assignments in a function store the value in the local symbol table;
whereas variable references first look in the local symbol table, then
in the global symbol table, and then in the table of built-in names.
Thus,
global variables cannot be directly assigned a value within a
-function (unless named in a {\tt global} statement), although
+function (unless named in a \code{global} statement), although
they may be referenced.
The actual parameters (arguments) to a function call are introduced in
the local symbol table of the called function when it is called; thus,
-arguments are passed using {\em call\ by\ value}.%
+arguments are passed using \emph{call by value}.%
\footnote{
- Actually, {\em call by object reference} would be a better
+ Actually, \emph{call by object reference} would be a better
description, since if a mutable object is passed, the caller
will see any changes the callee makes to it (e.g., items
inserted into a list).
@@ -1094,11 +1094,11 @@
>>>
\end{verbatim}\ecode
%
-You might object that {\tt fib} is not a function but a procedure. In
+You might object that \code{fib} is not a function but a procedure. In
Python, like in C, procedures are just functions that don't return a
value. In fact, technically speaking, procedures do return a value,
-albeit a rather boring one. This value is called {\tt None} (it's a
-built-in name). Writing the value {\tt None} is normally suppressed by
+albeit a rather boring one. This value is called \code{None} (it's a
+built-in name). Writing the value \code{None} is normally suppressed by
the interpreter if it would be the only value written. You can see it
if you really want to:
@@ -1117,8 +1117,8 @@
... result = []
... a, b = 0, 1
... while b < n:
-... result.append(b) # see below
-... a, b = b, a+b
+... result.append(b) # see below
+... a, b = b, a+b
... return result
...
>>> f100 = fib2(100) # call it
@@ -1132,25 +1132,25 @@
\begin{itemize}
\item
-The {\tt return} statement returns with a value from a function. {\tt
-return} without an expression argument is used to return from the middle
-of a procedure (falling off the end also returns from a procedure), in
-which case the {\tt None} value is returned.
+The \code{return} statement returns with a value from a function.
+\code{return} without an expression argument is used to return from
+the middle of a procedure (falling off the end also returns from a
+procedure), in which case the \code{None} value is returned.
\item
-The statement {\tt result.append(b)} calls a {\em method} of the list
-object {\tt result}. A method is a function that `belongs' to an
-object and is named {\tt obj.methodname}, where {\tt obj} is some
-object (this may be an expression), and {\tt methodname} is the name
+The statement \code{result.append(b)} calls a \emph{method} of the list
+object \code{result}. A method is a function that `belongs' to an
+object and is named \code{obj.methodname}, where \code{obj} is some
+object (this may be an expression), and \code{methodname} is the name
of a method that is defined by the object's type. Different types
define different methods. Methods of different types may have the
same name without causing ambiguity. (It is possible to define your
-own object types and methods, using {\em classes}, as discussed later
+own object types and methods, using \emph{classes}, as discussed later
in this tutorial.)
-The method {\tt append} shown in the example, is defined for
+The method \code{append} shown in the example, is defined for
list objects; it adds a new element at the end of the list. In this
example
-it is equivalent to {\tt result = result + [b]}, but more efficient.
+it is equivalent to \code{result = result + [b]}, but more efficient.
\end{itemize}
@@ -1166,31 +1166,31 @@
arguments than it is defined, e.g.
\begin{verbatim}
- def ask_ok(prompt, retries = 4, complaint = 'Yes or no, please!'):
- while 1:
- ok = raw_input(prompt)
- if ok in ('y', 'ye', 'yes'): return 1
- if ok in ('n', 'no', 'nop', 'nope'): return 0
- retries = retries - 1
- if retries < 0: raise IOError, 'refusenik user'
- print complaint
+ def ask_ok(prompt, retries=4, complaint='Yes or no, please!'):
+ while 1:
+ ok = raw_input(prompt)
+ if ok in ('y', 'ye', 'yes'): return 1
+ if ok in ('n', 'no', 'nop', 'nope'): return 0
+ retries = retries - 1
+ if retries < 0: raise IOError, 'refusenik user'
+ print complaint
\end{verbatim}
This function can be called either like this:
-\verb\ask_ok('Do you really want to quit?')\ or like this:
-\verb\ask_ok('OK to overwrite the file?', 2)\.
+\code{ask_ok('Do you really want to quit?')} or like this:
+\code{ask_ok('OK to overwrite the file?', 2)}.
The default values are evaluated at the point of function definition
-in the {\em defining} scope, so that e.g.
+in the \emph{defining} scope, so that e.g.
\begin{verbatim}
- i = 5
- def f(arg = i): print arg
- i = 6
- f()
+ i = 5
+ def f(arg = i): print arg
+ i = 6
+ f()
\end{verbatim}
-will print \verb\5\.
+will print \code{5}.
\subsection{Keyword Arguments}
@@ -1280,8 +1280,8 @@
of arguments, zero or more normal arguments may occur.
\begin{verbatim}
- def fprintf(file, format, *args):
- file.write(format % args)
+ def fprintf(file, format, *args):
+ file.write(format % args)
\end{verbatim}
\chapter{Data Structures}
@@ -1296,31 +1296,31 @@
\begin{description}
-\item[{\tt insert(i, x)}]
+\item[\code{insert(i, x)}]
Insert an item at a given position. The first argument is the index of
-the element before which to insert, so {\tt a.insert(0, x)} inserts at
-the front of the list, and {\tt a.insert(len(a), x)} is equivalent to
-{\tt a.append(x)}.
+the element before which to insert, so \code{a.insert(0, x)} inserts at
+the front of the list, and \code{a.insert(len(a), x)} is equivalent to
+\code{a.append(x)}.
-\item[{\tt append(x)}]
-Equivalent to {\tt a.insert(len(a), x)}.
+\item[\code{append(x)}]
+Equivalent to \code{a.insert(len(a), x)}.
-\item[{\tt index(x)}]
-Return the index in the list of the first item whose value is {\tt x}.
+\item[\code{index(x)}]
+Return the index in the list of the first item whose value is \code{x}.
It is an error if there is no such item.
-\item[{\tt remove(x)}]
-Remove the first item from the list whose value is {\tt x}.
+\item[\code{remove(x)}]
+Remove the first item from the list whose value is \code{x}.
It is an error if there is no such item.
-\item[{\tt sort()}]
+\item[\code{sort()}]
Sort the items of the list, in place.
-\item[{\tt reverse()}]
+\item[\code{reverse()}]
Reverse the elements of the list, in place.
-\item[{\tt count(x)}]
-Return the number of times {\tt x} appears in the list.
+\item[\code{count(x)}]
+Return the number of times \code{x} appears in the list.
\end{description}
@@ -1351,31 +1351,31 @@
\subsection{Functional Programming Tools}
There are three built-in functions that are very useful when used with
-lists: \verb\filter\, \verb\map\, and \verb\reduce\.
+lists: \code{filter()}, \code{map()}, and \code{reduce()}.
-\verb\filter(function, sequence)\ returns a sequence (of the same
+\code{filter(function, sequence)} returns a sequence (of the same
type, if possible) consisting of those items from the sequence for
-which \verb\function(item)\ is true. For example, to compute some
+which \code{function(item)} is true. For example, to compute some
primes:
\begin{verbatim}
- >>> def f(x): return x%2 != 0 and x%3 != 0
- ...
- >>> filter(f, range(2, 25))
- [5, 7, 11, 13, 17, 19, 23]
- >>>
+ >>> def f(x): return x%2 != 0 and x%3 != 0
+ ...
+ >>> filter(f, range(2, 25))
+ [5, 7, 11, 13, 17, 19, 23]
+ >>>
\end{verbatim}
-\verb\map(function, sequence)\ calls \verb\function(item)\ for each of
+\code{map(function, sequence)} calls \code{function(item)} for each of
the sequence's items and returns a list of the return values. For
example, to compute some cubes:
\begin{verbatim}
- >>> def cube(x): return x*x*x
- ...
- >>> map(cube, range(1, 11))
- [1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]
- >>>
+ >>> def cube(x): return x*x*x
+ ...
+ >>> map(cube, range(1, 11))
+ [1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]
+ >>>
\end{verbatim}
More than one sequence may be passed; the function must then have as
@@ -1389,12 +1389,12 @@
of lists into a list of pairs. For example:
\begin{verbatim}
- >>> seq = range(8)
- >>> def square(x): return x*x
- ...
- >>> map(None, seq, map(square, seq))
- [(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25), (6, 36), (7, 49)]
- >>>
+ >>> seq = range(8)
+ >>> def square(x): return x*x
+ ...
+ >>> map(None, seq, map(square, seq))
+ [(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25), (6, 36), (7, 49)]
+ >>>
\end{verbatim}
\verb\reduce(func, sequence)\ returns a single value constructed
@@ -1403,11 +1403,11 @@
example, to compute the sum of the numbers 1 through 10:
\begin{verbatim}
- >>> def add(x,y): return x+y
- ...
- >>> reduce(add, range(1, 11))
- 55
- >>>
+ >>> def add(x,y): return x+y
+ ...
+ >>> reduce(add, range(1, 11))
+ 55
+ >>>
\end{verbatim}
If there's only one item in the sequence, its value is returned; if
@@ -1419,21 +1419,21 @@
item, then to the result and the next item, and so on. For example,
\begin{verbatim}
- >>> def sum(seq):
- ... def add(x,y): return x+y
- ... return reduce(add, seq, 0)
- ...
- >>> sum(range(1, 11))
- 55
- >>> sum([])
- 0
- >>>
+ >>> def sum(seq):
+ ... def add(x,y): return x+y
+ ... return reduce(add, seq, 0)
+ ...
+ >>> sum(range(1, 11))
+ 55
+ >>> sum([])
+ 0
+ >>>
\end{verbatim}
-\section{The {\tt del} statement}
+\section{The \sectcode{del} statement}
There is a way to remove an item from a list given its index instead
-of its value: the {\tt del} statement. This can also be used to
+of its value: the \code{del} statement. This can also be used to
remove slices from a list (which we did earlier by assignment of an
empty list to the slice). For example:
@@ -1449,24 +1449,24 @@
>>>
\end{verbatim}\ecode
%
-{\tt del} can also be used to delete entire variables:
+\code{del} can also be used to delete entire variables:
\bcode\begin{verbatim}
>>> del a
>>>
\end{verbatim}\ecode
%
-Referencing the name {\tt a} hereafter is an error (at least until
-another value is assigned to it). We'll find other uses for {\tt del}
+Referencing the name \code{a} hereafter is an error (at least until
+another value is assigned to it). We'll find other uses for \code{del}
later.
\section{Tuples and Sequences}
We saw that lists and strings have many common properties, e.g.,
-indexing and slicing operations. They are two examples of {\em
-sequence} data types. Since Python is an evolving language, other
-sequence data types may be added. There is also another standard
-sequence data type: the {\em tuple}.
+indexing and slicing operations. They are two examples of
+\emph{sequence} data types. Since Python is an evolving language,
+other sequence data types may be added. There is also another
+standard sequence data type: the \emph{tuple}.
A tuple consists of a number of values separated by commas, for
instance:
@@ -1514,23 +1514,23 @@
>>>
\end{verbatim}\ecode
%
-The statement {\tt t = 12345, 54321, 'hello!'} is an example of {\em
-tuple packing}: the values {\tt 12345}, {\tt 54321} and {\tt 'hello!'}
-are packed together in a tuple. The reverse operation is also
-possible, e.g.:
+The statement \code{t = 12345, 54321, 'hello!'} is an example of
+\emph{tuple packing}: the values \code{12345}, \code{54321} and
+\code{'hello!'} are packed together in a tuple. The reverse operation
+is also possible, e.g.:
\bcode\begin{verbatim}
>>> x, y, z = t
>>>
\end{verbatim}\ecode
%
-This is called, appropriately enough, {\em tuple unpacking}. Tuple
+This is called, appropriately enough, \emph{tuple unpacking}. Tuple
unpacking requires that the list of variables on the left has the same
number of elements as the length of the tuple. Note that multiple
assignment is really just a combination of tuple packing and tuple
unpacking!
-Occasionally, the corresponding operation on lists is useful: {\em list
+Occasionally, the corresponding operation on lists is useful: \emph{list
unpacking}. This is supported by enclosing the list of variables in
square brackets:
@@ -1542,19 +1542,19 @@
\section{Dictionaries}
-Another useful data type built into Python is the {\em dictionary}.
+Another useful data type built into Python is the \emph{dictionary}.
Dictionaries are sometimes found in other languages as ``associative
memories'' or ``associative arrays''. Unlike sequences, which are
-indexed by a range of numbers, dictionaries are indexed by {\em keys},
+indexed by a range of numbers, dictionaries are indexed by \emph{keys},
which can be any non-mutable type; strings and numbers can always be
keys. Tuples can be used as keys if they contain only strings,
numbers, or tuples. You can't use lists as keys, since lists can be
modified in place using their \code{append()} method.
It is best to think of a dictionary as an unordered set of
-{\em key:value} pairs, with the requirement that the keys are unique
+\emph{key:value} pairs, with the requirement that the keys are unique
(within one dictionary).
-A pair of braces creates an empty dictionary: \verb/{}/.
+A pair of braces creates an empty dictionary: \code{\{\}}.
Placing a comma-separated list of key:value pairs within the
braces adds initial key:value pairs to the dictionary; this is also the
way dictionaries are written on output.
@@ -1562,15 +1562,15 @@
The main operations on a dictionary are storing a value with some key
and extracting the value given the key. It is also possible to delete
a key:value pair
-with {\tt del}.
+with \code{del}.
If you store using a key that is already in use, the old value
associated with that key is forgotten. It is an error to extract a
value using a non-existent key.
-The {\tt keys()} method of a dictionary object returns a list of all the
+The \code{keys()} method of a dictionary object returns a list of all the
keys used in the dictionary, in random order (if you want it sorted,
-just apply the {\tt sort()} method to the list of keys). To check
-whether a single key is in the dictionary, use the \verb/has_key()/
+just apply the \code{sort()} method to the list of keys). To check
+whether a single key is in the dictionary, use the \code{has_key()}
method of the dictionary.
Here is a small example using a dictionary:
@@ -1595,34 +1595,34 @@
\section{More on Conditions}
-The conditions used in {\tt while} and {\tt if} statements above can
+The conditions used in \code{while} and \code{if} statements above can
contain other operators besides comparisons.
-The comparison operators {\tt in} and {\tt not in} check whether a value
-occurs (does not occur) in a sequence. The operators {\tt is} and {\tt
-is not} compare whether two objects are really the same object; this
+The comparison operators \code{in} and \code{not in} check whether a value
+occurs (does not occur) in a sequence. The operators \code{is} and
+\code{is not} compare whether two objects are really the same object; this
only matters for mutable objects like lists. All comparison operators
have the same priority, which is lower than that of all numerical
operators.
-Comparisons can be chained: e.g., {\tt a < b == c} tests whether {\tt a}
-is less than {\tt b} and moreover {\tt b} equals {\tt c}.
+Comparisons can be chained: e.g., \code{a < b == c} tests whether \code{a}
+is less than \code{b} and moreover \code{b} equals \code{c}.
-Comparisons may be combined by the Boolean operators {\tt and} and {\tt
-or}, and the outcome of a comparison (or of any other Boolean
-expression) may be negated with {\tt not}. These all have lower
-priorities than comparison operators again; between them, {\tt not} has
-the highest priority, and {\tt or} the lowest, so that
-{\tt A and not B or C} is equivalent to {\tt (A and (not B)) or C}. Of
+Comparisons may be combined by the Boolean operators \code{and} and
+\code{or}, and the outcome of a comparison (or of any other Boolean
+expression) may be negated with \code{not}. These all have lower
+priorities than comparison operators again; between them, \code{not} has
+the highest priority, and \code{or} the lowest, so that
+\code{A and not B or C} is equivalent to \code{(A and (not B)) or C}. Of
course, parentheses can be used to express the desired composition.
-The Boolean operators {\tt and} and {\tt or} are so-called {\em
-shortcut} operators: their arguments are evaluated from left to right,
-and evaluation stops as soon as the outcome is determined. E.g., if
-{\tt A} and {\tt C} are true but {\tt B} is false, {\tt A and B and C}
-does not evaluate the expression C. In general, the return value of a
-shortcut operator, when used as a general value and not as a Boolean, is
-the last evaluated argument.
+The Boolean operators \code{and} and \code{or} are so-called
+\emph{shortcut} operators: their arguments are evaluated from left to
+right, and evaluation stops as soon as the outcome is determined.
+E.g., if \code{A} and \code{C} are true but \code{B} is false, \code{A
+and B and C} does not evaluate the expression C. In general, the
+return value of a shortcut operator, when used as a general value and
+not as a Boolean, is the last evaluated argument.
It is possible to assign the result of a comparison or other Boolean
expression to a variable. For example,
@@ -1640,7 +1640,7 @@
\section{Comparing Sequences and Other Types}
Sequence objects may be compared to other objects with the same
-sequence type. The comparison uses {\em lexicographical} ordering:
+sequence type. The comparison uses \emph{lexicographical} ordering:
first the first two items are compared, and if they differ this
determines the outcome of the comparison; if they are equal, the next
two items are compared, and so on, until either sequence is exhausted.
@@ -1681,24 +1681,24 @@
Therefore, if you want to write a somewhat longer program, you are
better off using a text editor to prepare the input for the interpreter
and running it with that file as input instead. This is known as creating a
-{\em script}. As your program gets longer, you may want to split it
+\emph{script}. As your program gets longer, you may want to split it
into several files for easier maintenance. You may also want to use a
handy function that you've written in several programs without copying
its definition into each program.
To support this, Python has a way to put definitions in a file and use
them in a script or in an interactive instance of the interpreter.
-Such a file is called a {\em module}; definitions from a module can be
-{\em imported} into other modules or into the {\em main} module (the
+Such a file is called a \emph{module}; definitions from a module can be
+\emph{imported} into other modules or into the \emph{main} module (the
collection of variables that you have access to in a script
executed at the top level
and in calculator mode).
A module is a file containing Python definitions and statements. The
-file name is the module name with the suffix {\tt .py} appended. Within
+file name is the module name with the suffix \file{.py} appended. Within
a module, the module's name (as a string) is available as the value of
-the global variable {\tt __name__}. For instance, use your favorite text
-editor to create a file called {\tt fibo.py} in the current directory
+the global variable \code{__name__}. For instance, use your favorite text
+editor to create a file called \file{fibo.py} in the current directory
with the following contents:
\bcode\begin{verbatim}
@@ -1707,15 +1707,15 @@
def fib(n): # write Fibonacci series up to n
a, b = 0, 1
while b < n:
- print b,
- a, b = b, a+b
+ print b,
+ a, b = b, a+b
def fib2(n): # return Fibonacci series up to n
result = []
a, b = 0, 1
while b < n:
- result.append(b)
- a, b = b, a+b
+ result.append(b)
+ a, b = b, a+b
return result
\end{verbatim}\ecode
%
@@ -1728,9 +1728,9 @@
\end{verbatim}\ecode
%
This does not enter the names of the functions defined in
-{\tt fibo}
+\code{fibo}
directly in the current symbol table; it only enters the module name
-{\tt fibo}
+\code{fibo}
there.
Using the module name you can access the functions:
@@ -1760,7 +1760,7 @@
definitions.
These statements are intended to initialize the module.
They are executed only the
-{\em first}
+\emph{first}
time the module is imported somewhere.%
\footnote{
In fact function definitions are also `statements' that are
@@ -1776,17 +1776,17 @@
On the other hand, if you know what you are doing you can touch a
module's global variables with the same notation used to refer to its
functions,
-{\tt modname.itemname}.
+\code{modname.itemname}.
Modules can import other modules.
It is customary but not required to place all
-{\tt import}
+\code{import}
statements at the beginning of a module (or script, for that matter).
The imported module names are placed in the importing module's global
symbol table.
There is a variant of the
-{\tt import}
+\code{import}
statement that imports names from a module directly into the importing
module's symbol table.
For example:
@@ -1799,7 +1799,7 @@
\end{verbatim}\ecode
%
This does not introduce the module name from which the imports are taken
-in the local symbol table (so in the example, {\tt fibo} is not
+in the local symbol table (so in the example, \code{fibo} is not
defined).
There is even a variant to import all names that a module defines:
@@ -1812,45 +1812,45 @@
\end{verbatim}\ecode
%
This imports all names except those beginning with an underscore
-({\tt _}).
+(\code{_}).
\subsection{The Module Search Path}
-When a module named {\tt spam} is imported, the interpreter searches
-for a file named {\tt spam.py} in the current directory,
+When a module named \code{spam} is imported, the interpreter searches
+for a file named \file{spam.py} in the current directory,
and then in the list of directories specified by
-the environment variable {\tt PYTHONPATH}. This has the same syntax as
-the \UNIX{} shell variable {\tt PATH}, i.e., a list of colon-separated
-directory names. When {\tt PYTHONPATH} is not set, or when the file
+the environment variable \code{PYTHONPATH}. This has the same syntax as
+the \UNIX{} shell variable \code{PATH}, i.e., a list of colon-separated
+directory names. When \code{PYTHONPATH} is not set, or when the file
is not found there, the search continues in an installation-dependent
-default path, usually {\tt .:/usr/local/lib/python}.
+default path, usually \code{.:/usr/local/lib/python}.
Actually, modules are searched in the list of directories given by the
-variable {\tt sys.path} which is initialized from the directory
-containing the input script (or the current directory), {\tt
-PYTHONPATH} and the installation-dependent default. This allows
+variable \code{sys.path} which is initialized from the directory
+containing the input script (or the current directory),
+\code{PYTHONPATH} and the installation-dependent default. This allows
Python programs that know what they're doing to modify or replace the
module search path. See the section on Standard Modules later.
\subsection{``Compiled'' Python files}
As an important speed-up of the start-up time for short programs that
-use a lot of standard modules, if a file called {\tt spam.pyc} exists
-in the directory where {\tt spam.py} is found, this is assumed to
-contain an already-``compiled'' version of the module {\tt spam}. The
-modification time of the version of {\tt spam.py} used to create {\tt
-spam.pyc} is recorded in {\tt spam.pyc}, and the file is ignored if
-these don't match.
+use a lot of standard modules, if a file called \file{spam.pyc} exists
+in the directory where \file{spam.py} is found, this is assumed to
+contain an already-``compiled'' version of the module \code{spam}. The
+modification time of the version of \file{spam.py} used to create
+\file{spam.pyc} is recorded in \file{spam.pyc}, and the file is
+ignored if these don't match.
-Normally, you don't need to do anything to create the {\tt spam.pyc} file.
-Whenever {\tt spam.py} is successfully compiled, an attempt is made to
-write the compiled version to {\tt spam.pyc}. It is not an error if
+Normally, you don't need to do anything to create the \file{spam.pyc} file.
+Whenever \file{spam.py} is successfully compiled, an attempt is made to
+write the compiled version to \file{spam.pyc}. It is not an error if
this attempt fails; if for any reason the file is not written
-completely, the resulting {\tt spam.pyc} file will be recognized as
-invalid and thus ignored later. The contents of the {\tt spam.pyc}
+completely, the resulting \file{spam.pyc} file will be recognized as
+invalid and thus ignored later. The contents of the \file{spam.pyc}
file is platform independent, so a Python module directory can be
shared by machines of different architectures. (Tip for experts:
-the module {\tt compileall} creates {\tt .pyc} files for all modules.)
+the module \code{compileall} creates file{.pyc} files for all modules.)
XXX Should optimization with -O be covered here?
@@ -1862,11 +1862,11 @@
core of the language but are nevertheless built in, either for
efficiency or to provide access to operating system primitives such as
system calls. The set of such modules is a configuration option; e.g.,
-the {\tt amoeba} module is only provided on systems that somehow support
-Amoeba primitives. One particular module deserves some attention: {\tt
-sys}, which is built into every Python interpreter. The variables {\tt
-sys.ps1} and {\tt sys.ps2} define the strings used as primary and
-secondary prompts:
+the \code{amoeba} module is only provided on systems that somehow support
+Amoeba primitives. One particular module deserves some attention:
+\code{sys}, which is built into every Python interpreter. The
+variables \code{sys.ps1} and \code{sys.ps2} define the strings used as
+primary and secondary prompts:
\bcode\begin{verbatim}
>>> import sys
@@ -1884,13 +1884,13 @@
interactive mode.
The variable
-{\tt sys.path}
+\code{sys.path}
is a list of strings that determine the interpreter's search path for
modules.
It is initialized to a default path taken from the environment variable
-{\tt PYTHONPATH},
+\code{PYTHONPATH},
or from a built-in default if
-{\tt PYTHONPATH}
+\code{PYTHONPATH}
is not set.
You can modify it using standard list operations, e.g.:
@@ -1900,9 +1900,9 @@
>>>
\end{verbatim}\ecode
-\section{The {\tt dir()} function}
+\section{The \sectcode{dir()} function}
-The built-in function {\tt dir} is used to find out which names a module
+The built-in function \code{dir()} is used to find out which names a module
defines. It returns a sorted list of strings:
\bcode\begin{verbatim}
@@ -1916,7 +1916,7 @@
>>>
\end{verbatim}\ecode
%
-Without arguments, {\tt dir()} lists the names you have defined currently:
+Without arguments, \code{dir()} lists the names you have defined currently:
\bcode\begin{verbatim}
>>> a = [1, 2, 3, 4, 5]
@@ -1929,9 +1929,9 @@
%
Note that it lists all types of names: variables, modules, functions, etc.
-{\tt dir()} does not list the names of built-in functions and variables.
+\code{dir()} does not list the names of built-in functions and variables.
If you want a list of those, they are defined in the standard module
-{\tt __builtin__}:
+\code{__builtin__}:
\bcode\begin{verbatim}
>>> import __builtin__
@@ -1956,28 +1956,28 @@
This chapter will discuss some of the possibilities.
\section{Fancier Output Formatting}
-So far we've encountered two ways of writing values: {\em expression
-statements} and the {\tt print} statement. (A third way is using the
-{\tt write} method of file objects; the standard output file can be
-referenced as {\tt sys.stdout}. See the Library Reference for more
+So far we've encountered two ways of writing values: \emph{expression
+statements} and the \code{print} statement. (A third way is using the
+\code{write} method of file objects; the standard output file can be
+referenced as \code{sys.stdout}. See the Library Reference for more
information on this.)
Often you'll want more control over the formatting of your output than
simply printing space-separated values. There are two ways to format
your output; the first way is to do all the string handling yourself;
using string slicing and concatenation operations you can create any
-lay-out you can imagine. The standard module {\tt string} contains
+lay-out you can imagine. The standard module \code{string} contains
some useful operations for padding strings to a given column width;
these will be discussed shortly. The second way is to use the
\code{\%} operator with a string as the left argument. \code{\%}
-interprets the left argument as a \C\ \code{sprintf()}-style format
+interprets the left argument as a \C{} \code{sprintf()}-style format
string to be applied to the right argument, and returns the string
resulting from this formatting operation.
One question remains, of course: how do you convert values to strings?
Luckily, Python has a way to convert any value to a string: pass it to
-the \verb/repr()/ function, or just write the value between reverse
-quotes (\verb/``/). Some examples:
+the \code{repr()} function, or just write the value between reverse
+quotes (\code{``}). Some examples:
\bcode\begin{verbatim}
>>> x = 10 * 3.14
@@ -2036,20 +2036,20 @@
>>>
\end{verbatim}\ecode
%
-(Note that one space between each column was added by the way {\tt print}
+(Note that one space between each column was added by the way \code{print}
works: it always adds spaces between its arguments.)
-This example demonstrates the function {\tt string.rjust()}, which
+This example demonstrates the function \code{string.rjust()}, which
right-justifies a string in a field of a given width by padding it with
-spaces on the left. There are similar functions {\tt string.ljust()}
-and {\tt string.center()}. These functions do not write anything, they
+spaces on the left. There are similar functions \code{string.ljust()}
+and \code{string.center()}. These functions do not write anything, they
just return a new string. If the input string is too long, they don't
truncate it, but return it unchanged; this will mess up your column
lay-out but that's usually better than the alternative, which would be
lying about a value. (If you really want truncation you can always add
-a slice operation, as in {\tt string.ljust(x,~n)[0:n]}.)
+a slice operation, as in \code{string.ljust(x,~n)[0:n]}.)
-There is another function, {\tt string.zfill}, which pads a numeric
+There is another function, \code{string.zfill()}, which pads a numeric
string on the left with zeros. It understands about plus and minus
signs:
@@ -2066,24 +2066,24 @@
Using the \code{\%} operator looks like this:
\begin{verbatim}
- >>> import math
- >>> print 'The value of PI is approximately %5.3f.' % math.pi
- The value of PI is approximately 3.142.
- >>>
+ >>> import math
+ >>> print 'The value of PI is approximately %5.3f.' % math.pi
+ The value of PI is approximately 3.142.
+ >>>
\end{verbatim}
If there is more than one format in the string you pass a tuple as
right operand, e.g.
\begin{verbatim}
- >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
- >>> for name, phone in table.items():
- ... print '%-10s ==> %10d' % (name, phone)
- ...
- Jack ==> 4098
- Dcab ==> 8637678
- Sjoerd ==> 4127
- >>>
+ >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
+ >>> for name, phone in table.items():
+ ... print '%-10s ==> %10d' % (name, phone)
+ ...
+ Jack ==> 4098
+ Dcab ==> 8637678
+ Sjoerd ==> 4127
+ >>>
\end{verbatim}
Most formats work exactly as in C and require that you pass the proper
@@ -2100,10 +2100,10 @@
an extension of C formats using the form \verb\%(name)format\, e.g.
\begin{verbatim}
- >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
- >>> print 'Jack: %(Jack)d; Sjoerd: %(Sjoerd)d; Dcab: %(Dcab)d' % table
- Jack: 4098; Sjoerd: 4127; Dcab: 8637678
- >>>
+ >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
+ >>> print 'Jack: %(Jack)d; Sjoerd: %(Sjoerd)d; Dcab: %(Dcab)d' % table
+ Jack: 4098; Sjoerd: 4127; Dcab: 8637678
+ >>>
\end{verbatim}
This is particularly useful in combination with the new built-in
@@ -2162,11 +2162,11 @@
\end{verbatim}\ecode
%
\code{f.readline()} reads a single line from the file; a newline
-character (\verb/\n/) is left at the end of the string, and is only
+character (\code{\\n}) is left at the end of the string, and is only
omitted on the last line of the file if the file doesn't end in a
newline. This makes the return value unambiguous; if
\code{f.readline()} returns an empty string, the end of the file has
-been reached, while a blank line is represented by \verb/'\n'/, a
+been reached, while a blank line is represented by \code{'\\n'}, a
string containing only a single newline.
\bcode\begin{verbatim}
@@ -2178,7 +2178,7 @@
''
\end{verbatim}\ecode
%
-\code{f.readlines()} uses {\code{f.readline()} repeatedly, and returns
+\code{f.readlines()} uses \code{f.readline()} repeatedly, and returns
a list containing all the lines of data in the file.
\bcode\begin{verbatim}
@@ -2284,8 +2284,8 @@
Until now error messages haven't been more than mentioned, but if you
have tried out the examples you have probably seen some. There are
-(at least) two distinguishable kinds of errors: {\em syntax\ errors}
-and {\em exceptions}.
+(at least) two distinguishable kinds of errors: \emph{syntax errors}
+and \emph{exceptions}.
\section{Syntax Errors}
@@ -2304,9 +2304,9 @@
The parser repeats the offending line and displays a little `arrow'
pointing at the earliest point in the line where the error was detected.
The error is caused by (or at least detected at) the token
-{\em preceding}
+\emph{preceding}
the arrow: in the example, the error is detected at the keyword
-{\tt print}, since a colon ({\tt :}) is missing before it.
+\code{print}, since a colon (\code{:}) is missing before it.
File name and line number are printed so you know where to look in case
the input came from a script.
@@ -2314,7 +2314,7 @@
Even if a statement or expression is syntactically correct, it may
cause an error when an attempt is made to execute it.
-Errors detected during execution are called {\em exceptions} and are
+Errors detected during execution are called \emph{exceptions} and are
not unconditionally fatal: you will soon learn how to handle them in
Python programs. Most exceptions are not handled by programs,
however, and result in error messages as shown here:
@@ -2338,10 +2338,10 @@
The last line of the error message indicates what happened.
Exceptions come in different types, and the type is printed as part of
the message: the types in the example are
-{\tt ZeroDivisionError},
-{\tt NameError}
+\code{ZeroDivisionError},
+\code{NameError}
and
-{\tt TypeError}.
+\code{TypeError}.
The string printed as the exception type is the name of the built-in
name for the exception that occurred. This is true for all built-in
exceptions, but need not be true for user-defined exceptions (although
@@ -2382,35 +2382,35 @@
>>>
\end{verbatim}\ecode
%
-The {\tt try} statement works as follows.
+The \code{try} statement works as follows.
\begin{itemize}
\item
First, the
-{\em try\ clause}
-(the statement(s) between the {\tt try} and {\tt except} keywords) is
+\emph{try\ clause}
+(the statement(s) between the \code{try} and \code{except} keywords) is
executed.
\item
If no exception occurs, the
-{\em except\ clause}
-is skipped and execution of the {\tt try} statement is finished.
+\emph{except\ clause}
+is skipped and execution of the \code{try} statement is finished.
\item
If an exception occurs during execution of the try clause,
the rest of the clause is skipped. Then if
-its type matches the exception named after the {\tt except} keyword,
+its type matches the exception named after the \code{except} keyword,
the rest of the try clause is skipped, the except clause is executed,
-and then execution continues after the {\tt try} statement.
+and then execution continues after the \code{try} statement.
\item
If an exception occurs which does not match the exception named in the
except clause, it is passed on to outer try statements; if no handler is
found, it is an
-{\em unhandled\ exception}
+\emph{unhandled exception}
and execution stops with a message as shown above.
\end{itemize}
-A {\tt try} statement may have more than one except clause, to specify
+A \code{try} statement may have more than one except clause, to specify
handlers for different exceptions.
At most one handler will be executed.
Handlers only handle exceptions that occur in the corresponding try
-clause, not in other handlers of the same {\tt try} statement.
+clause, not in other handlers of the same \code{try} statement.
An except clause may name multiple exceptions as a parenthesized list,
e.g.:
@@ -2430,20 +2430,20 @@
exception. For example:
\begin{verbatim}
- for arg in sys.argv:
- try:
- f = open(arg, 'r')
- except IOError:
- print 'cannot open', arg
- else:
- print arg, 'has', len(f.readlines()), 'lines'
- f.close()
+ for arg in sys.argv:
+ try:
+ f = open(arg, 'r')
+ except IOError:
+ print 'cannot open', arg
+ else:
+ print arg, 'has', len(f.readlines()), 'lines'
+ f.close()
\end{verbatim}
When an exception occurs, it may have an associated value, also known as
the exceptions's
-{\em argument}.
+\emph{argument}.
The presence and type of the argument depend on the exception type.
For exception types which have an argument, the except clause may
specify a variable after the exception name (or list) to receive the
@@ -2483,7 +2483,7 @@
\section{Raising Exceptions}
-The {\tt raise} statement allows the programmer to force a specified
+The \code{raise} statement allows the programmer to force a specified
exception to occur.
For example:
@@ -2495,7 +2495,7 @@
>>>
\end{verbatim}\ecode
%
-The first argument to {\tt raise} names the exception to be raised.
+The first argument to \code{raise} names the exception to be raised.
The optional second argument specifies the exception's argument.
%
@@ -2528,7 +2528,7 @@
\section{Defining Clean-up Actions}
-The {\tt try} statement has another optional clause which is intended to
+The \code{try} statement has another optional clause which is intended to
define clean-up actions that must be executed under all circumstances.
For example:
@@ -2545,15 +2545,15 @@
>>>
\end{verbatim}\ecode
%
-A {\tt finally} clause is executed whether or not an exception has
-occurred in the {\tt try} clause. When an exception has occurred, it
-is re-raised after the {\tt finally} clause is executed. The
-{\tt finally} clause is also executed ``on the way out'' when the
-{\tt try} statement is left via a {\tt break} or {\tt return}
+A \code{finally} clause is executed whether or not an exception has
+occurred in the \code{try} clause. When an exception has occurred, it
+is re-raised after the \code{finally} clause is executed. The
+\code{finally} clause is also executed ``on the way out'' when the
+\code{try} statement is left via a \code{break} or \code{return}
statement.
-A {\tt try} statement must either have one or more {\tt except}
-clauses or one {\tt finally} clause, but not both.
+A \code{try} statement must either have one or more \code{except}
+clauses or one \code{finally} clause, but not both.
\chapter{Classes}
@@ -2569,7 +2569,7 @@
same name. Objects can contain an arbitrary amount of private data.
In \Cpp{} terminology, all class members (including the data members) are
-{\em public}, and all member functions are {\em virtual}. There are
+\emph{public}, and all member functions are \emph{virtual}. There are
no special constructors or destructors. As in Modula-3, there are no
shorthands for referencing the object's members from its methods: the
method function is declared with an explicit first argument
@@ -2594,7 +2594,7 @@
necessarily mean a class instance. Like \Cpp{} and Modula-3, and unlike
Smalltalk, not all types in Python are classes: the basic built-in
types like integers and lists aren't, and even somewhat more exotic
-types like files aren't. However, {\em all} Python types share a little
+types like files aren't. However, \emph{all} Python types share a little
bit of common semantics that is best described by using the word
object.
@@ -2624,7 +2624,7 @@
Let's begin with some definitions.
-A {\em name space} is a mapping from names to objects. Most name
+A \emph{name space} is a mapping from names to objects. Most name
spaces are currently implemented as Python dictionaries, but that's
normally not noticeable in any way (except for performance), and it
may change in the future. Examples of name spaces are: the set of
@@ -2637,7 +2637,7 @@
define a function ``maximize'' without confusion --- users of the
modules must prefix it with the module name.
-By the way, I use the word {\em attribute} for any name following a
+By the way, I use the word \emph{attribute} for any name following a
dot --- for example, in the expression \verb\z.real\, \verb\real\ is
an attribute of the object \verb\z\. Strictly speaking, references to
names in modules are attribute references: in the expression
@@ -2647,9 +2647,9 @@
global names defined in the module: they share the same name space!%
\footnote{
Except for one thing. Module objects have a secret read-only
- attribute called {\tt __dict__} which returns the dictionary
+ attribute called \code{__dict__} which returns the dictionary
used to implement the module's name space; the name
- {\tt __dict__} is an attribute but not a global name.
+ \code{__dict__} is an attribute but not a global name.
Obviously, using this violates the abstraction of name space
implementation, and should be restricted to things like
post-mortem debuggers...
@@ -2678,7 +2678,7 @@
be a better way to describe what actually happens.) Of course,
recursive invocations each have their own local name space.
-A {\em scope} is a textual region of a Python program where a name space
+A \emph{scope} is a textual region of a Python program where a name space
is directly accessible. ``Directly accessible'' here means that an
unqualified reference to a name attempts to find the name in the name
space.
@@ -2727,12 +2727,12 @@
The simplest form of class definition looks like this:
\begin{verbatim}
- class ClassName:
- <statement-1>
- .
- .
- .
- <statement-N>
+ class ClassName:
+ <statement-1>
+ .
+ .
+ .
+ <statement-N>
\end{verbatim}
Class definitions, like function definitions (\verb\def\ statements)
@@ -2752,7 +2752,7 @@
go into this new name space. In particular, function definitions bind
the name of the new function here.
-When a class definition is left normally (via the end), a {\em class
+When a class definition is left normally (via the end), a \emph{class
object} is created. This is basically a wrapper around the contents
of the name space created by the class definition; we'll learn more
about class objects in the next section. The original local scope
@@ -2766,18 +2766,18 @@
Class objects support two kinds of operations: attribute references
and instantiation.
-{\em Attribute references} use the standard syntax used for all
+\emph{Attribute references} use the standard syntax used for all
attribute references in Python: \verb\obj.name\. Valid attribute
names are all the names that were in the class's name space when the
class object was created. So, if the class definition looked like
this:
\begin{verbatim}
- class MyClass:
- "A simple example class"
- i = 12345
- def f(x):
- return 'hello world'
+ class MyClass:
+ "A simple example class"
+ i = 12345
+ def f(x):
+ return 'hello world'
\end{verbatim}
then \verb\MyClass.i\ and \verb\MyClass.f\ are valid attribute
@@ -2787,16 +2787,16 @@
attribute that's read-only, returning the docstring belonging to
the class: \verb\"A simple example class"\).
-Class {\em instantiation} uses function notation. Just pretend that
+Class \emph{instantiation} uses function notation. Just pretend that
the class object is a parameterless function that returns a new
instance of the class. For example, (assuming the above class):
\begin{verbatim}
- x = MyClass()
+ x = MyClass()
\end{verbatim}
-creates a new {\em instance} of the class and assigns this object to
-the local variable \verb\x\.
+creates a new \emph{instance} of the class and assigns this object to
+the local variable \code{x}.
\subsection{Instance objects}
@@ -2805,7 +2805,7 @@
understood by instance objects are attribute references. There are
two kinds of valid attribute names.
-The first I'll call {\em data attributes}. These correspond to
+The first I'll call \emph{data attributes}. These correspond to
``instance variables'' in Smalltalk, and to ``data members'' in \Cpp{}.
Data attributes need not be declared; like local variables, they
spring into existence when they are first assigned to. For example,
@@ -2814,15 +2814,15 @@
trace:
\begin{verbatim}
- x.counter = 1
- while x.counter < 10:
- x.counter = x.counter * 2
- print x.counter
- del x.counter
+ x.counter = 1
+ while x.counter < 10:
+ x.counter = x.counter * 2
+ print x.counter
+ del x.counter
\end{verbatim}
The second kind of attribute references understood by instance objects
-are {\em methods}. A method is a function that ``belongs to'' an
+are \emph{methods}. A method is a function that ``belongs to'' an
object. (In Python, the term method is not unique to class instances:
other object types can have methods as well, e.g., list objects have
methods called append, insert, remove, sort, and so on. However,
@@ -2832,10 +2832,10 @@
Valid method names of an instance object depend on its class. By
definition, all attributes of a class that are (user-defined) function
objects define corresponding methods of its instances. So in our
-example, \verb\x.f\ is a valid method reference, since
-\verb\MyClass.f\ is a function, but \verb\x.i\ is not, since
-\verb\MyClass.i\ is not. But \verb\x.f\ is not the
-same thing as \verb\MyClass.f\ --- it is a {\em method object}, not a
+example, \code{x.f} is a valid method reference, since
+\code{MyClass.f} is a function, but \code{x.i} is not, since
+\code{MyClass.i} is not. But \code{x.f} is not the
+same thing as \verb\MyClass.f\ --- it is a \emph{method object}, not a
function object.
@@ -2844,7 +2844,7 @@
Usually, a method is called immediately, e.g.:
\begin{verbatim}
- x.f()
+ x.f()
\end{verbatim}
In our example, this will return the string \verb\'hello world'\.
@@ -2853,9 +2853,9 @@
moment, for example:
\begin{verbatim}
- xf = x.f
- while 1:
- print xf()
+ xf = x.f
+ while 1:
+ print xf()
\end{verbatim}
will continue to print \verb\hello world\ until the end of time.
@@ -2871,7 +2871,7 @@
methods is that the object is passed as the first argument of the
function. In our example, the call \verb\x.f()\ is exactly equivalent
to \verb\MyClass.f(x)\. In general, calling a method with a list of
-{\em n} arguments is equivalent to calling the corresponding function
+\var{n} arguments is equivalent to calling the corresponding function
with an argument list that is created by inserting the method's object
before the first argument.
@@ -2930,7 +2930,7 @@
\verb\self\ has absolutely no special meaning to Python. (Note,
however, that by not following the convention your code may be less
readable by other Python programmers, and it is also conceivable that
-a {\em class browser} program be written which relies upon such a
+a \emph{class browser} program be written which relies upon such a
convention.)
@@ -2941,15 +2941,15 @@
example:
\begin{verbatim}
- # Function defined outside the class
- def f1(self, x, y):
- return min(x, x+y)
-
- class C:
- f = f1
- def g(self):
- return 'hello world'
- h = g
+ # Function defined outside the class
+ def f1(self, x, y):
+ return min(x, x+y)
+
+ class C:
+ f = f1
+ def g(self):
+ return 'hello world'
+ h = g
\end{verbatim}
Now \verb\f\, \verb\g\ and \verb\h\ are all attributes of class
@@ -2963,34 +2963,34 @@
\verb\self\ argument, e.g.:
\begin{verbatim}
- class Bag:
- def empty(self):
- self.data = []
- def add(self, x):
- self.data.append(x)
- def addtwice(self, x):
- self.add(x)
- self.add(x)
+ class Bag:
+ def empty(self):
+ self.data = []
+ def add(self, x):
+ self.data.append(x)
+ def addtwice(self, x):
+ self.add(x)
+ self.add(x)
\end{verbatim}
The instantiation operation (``calling'' a class object) creates an
empty object. Many classes like to create objects in a known initial
state. Therefore a class may define a special method named
-\verb\__init__\, like this:
+\code{__init__()}, like this:
\begin{verbatim}
- def __init__(self):
- self.empty()
+ def __init__(self):
+ self.empty()
\end{verbatim}
-When a class defines an \verb\__init__\ method, class instantiation
-automatically invokes \verb\__init__\ for the newly-created class
-instance. So in the \verb\Bag\ example, a new and initialized instance
+When a class defines an \code{__init__()} method, class instantiation
+automatically invokes \code{__init__()} for the newly-created class
+instance. So in the \code{Bag} example, a new and initialized instance
can be obtained by:
\begin{verbatim}
- x = Bag()
+ x = Bag()
\end{verbatim}
Of course, the \verb\__init__\ method may have arguments for greater
@@ -3028,12 +3028,12 @@
definition looks as follows:
\begin{verbatim}
- class DerivedClassName(BaseClassName):
- <statement-1>
- .
- .
- .
- <statement-N>
+ class DerivedClassName(BaseClassName):
+ <statement-1>
+ .
+ .
+ .
+ <statement-N>
\end{verbatim}
The name \verb\BaseClassName\ must be defined in a scope containing
@@ -3042,7 +3042,7 @@
defined in another module, e.g.,
\begin{verbatim}
- class DerivedClassName(modname.BaseClassName):
+ class DerivedClassName(modname.BaseClassName):
\end{verbatim}
Execution of a derived class definition proceeds the same as for a
@@ -3079,12 +3079,12 @@
class definition with multiple base classes looks as follows:
\begin{verbatim}
- class DerivedClassName(Base1, Base2, Base3):
- <statement-1>
- .
- .
- .
- <statement-N>
+ class DerivedClassName(Base1, Base2, Base3):
+ <statement-1>
+ .
+ .
+ .
+ <statement-N>
\end{verbatim}
The only rule necessary to explain the semantics is the resolution
@@ -3123,7 +3123,7 @@
is done without regard of the syntactic position of the identifier, so
it can be used to define class-private instance and class variables,
methods, as well as globals, and even to store instance variables
-private to this class on instances of {\em other} classes. Truncation
+private to this class on instances of \emph{other} classes. Truncation
may occur when the mangled name would be longer than 255 characters.
Outside classes, or when the class name consists of only underscores,
no mangling occurs.
@@ -3189,15 +3189,15 @@
items. An empty class definition will do nicely, e.g.:
\begin{verbatim}
- class Employee:
- pass
+ class Employee:
+ pass
- john = Employee() # Create an empty employee record
+ john = Employee() # Create an empty employee record
- # Fill the fields of the record
- john.name = 'John Doe'
- john.dept = 'computer lab'
- john.salary = 1000
+ # Fill the fields of the record
+ john.name = 'John Doe'
+ john.dept = 'computer lab'
+ john.salary = 1000
\end{verbatim}
@@ -3339,8 +3339,8 @@
overcome through the judicious use of default argument values, e.g.
\begin{verbatim}
- def make_incrementor(n):
- return lambda x, incr=n: x+incr
+ def make_incrementor(n):
+ return lambda x, incr=n: x+incr
\end{verbatim}
\section{Documentation Strings}
@@ -3368,7 +3368,7 @@
The Python parser does not strip indentation from multi-line string
literals in Python, so tools that process documentation have to strip
indentation. This is done using the following convention. The first
-non-blank line {\em after} the first line of the string determines the
+non-blank line \emph{after} the first line of the string determines the
amount of indentation for the entire documentation string. (We can't
use the first line since it is generally adjacent to the string's
opening quotes so its indentation is not apparent in the string
@@ -3384,7 +3384,7 @@
Some versions of the Python interpreter support editing of the current
input line and history substitution, similar to facilities found in
the Korn shell and the GNU Bash shell. This is implemented using the
-{\em GNU\ Readline} library, which supports Emacs-style and vi-style
+\emph{GNU Readline} library, which supports Emacs-style and vi-style
editing. This library has its own documentation which I won't
duplicate here; however, the basics are easily explained.
@@ -3416,7 +3416,7 @@
The key bindings and some other parameters of the Readline library can
be customized by placing commands in an initialization file called
-{\tt \$HOME/.inputrc}. Key bindings have the form
+\file{\$HOME/.inputrc}. Key bindings have the form
\bcode\begin{verbatim}
key-name: function-name
@@ -3455,7 +3455,7 @@
TAB: complete
\end{verbatim}\ecode
%
-in your {\tt \$HOME/.inputrc}. (Of course, this makes it hard to type
+in your \file{\$HOME/.inputrc}. (Of course, this makes it hard to type
indented continuation lines...)
\subsection{Commentary}