| \section{Built-in Functions \label{built-in-funcs}} |
| |
| The Python interpreter has a number of functions built into it that |
| are always available. They are listed here in alphabetical order. |
| |
| |
| \setindexsubitem{(built-in function)} |
| |
| \begin{funcdesc}{__import__}{name\optional{, globals\optional{, locals\optional{, fromlist}}}} |
| This function is invoked by the |
| \keyword{import}\stindex{import} statement. It mainly |
| exists so that you can replace it with another function that has a |
| compatible interface, in order to change the semantics of the |
| \keyword{import} statement. For examples of why and how you would do |
| this, see the standard library modules |
| \module{ihooks}\refstmodindex{ihooks} and |
| \refmodule{rexec}\refstmodindex{rexec}. See also the built-in module |
| \refmodule{imp}\refbimodindex{imp}, which defines some useful |
| operations out of which you can build your own |
| \function{__import__()} function. |
| |
| For example, the statement `\code{import} \code{spam}' results in the |
| following call: |
| \code{__import__('spam',} \code{globals(),} \code{locals(), [])}; |
| the statement \code{from} \code{spam.ham import} \code{eggs} results |
| in \code{__import__('spam.ham',} \code{globals(),} \code{locals(),} |
| \code{['eggs'])}. |
| Note that even though \code{locals()} and \code{['eggs']} are passed |
| in as arguments, the \function{__import__()} function does not set the |
| local variable named \code{eggs}; this is done by subsequent code that |
| is generated for the import statement. (In fact, the standard |
| implementation does not use its \var{locals} argument at all, and uses |
| its \var{globals} only to determine the package context of the |
| \keyword{import} statement.) |
| |
| When the \var{name} variable is of the form \code{package.module}, |
| normally, the top-level package (the name up till the first dot) is |
| returned, \emph{not} the module named by \var{name}. However, when a |
| non-empty \var{fromlist} argument is given, the module named by |
| \var{name} is returned. This is done for compatibility with the |
| bytecode generated for the different kinds of import statement; when |
| using \samp{import spam.ham.eggs}, the top-level package \code{spam} |
| must be placed in the importing namespace, but when using \samp{from |
| spam.ham import eggs}, the \code{spam.ham} subpackage must be used to |
| find the \code{eggs} variable. |
| As a workaround for this behavior, use \function{getattr()} to extract |
| the desired components. For example, you could define the following |
| helper: |
| |
| \begin{verbatim} |
| import string |
| |
| def my_import(name): |
| mod = __import__(name) |
| components = string.split(name, '.') |
| for comp in components[1:]: |
| mod = getattr(mod, comp) |
| return mod |
| \end{verbatim} |
| |
| \end{funcdesc} |
| |
| \begin{funcdesc}{abs}{x} |
| Return the absolute value of a number. The argument may be a plain |
| or long integer or a floating point number. If the argument is a |
| complex number, its magnitude is returned. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{apply}{function, args\optional{, keywords}} |
| The \var{function} argument must be a callable object (a user-defined or |
| built-in function or method, or a class object) and the \var{args} |
| argument must be a sequence (if it is not a tuple, the sequence is |
| first converted to a tuple). The \var{function} is called with |
| \var{args} as the argument list; the number of arguments is the the length |
| of the tuple. (This is different from just calling |
| \code{\var{func}(\var{args})}, since in that case there is always |
| exactly one argument.) |
| If the optional \var{keywords} argument is present, it must be a |
| dictionary whose keys are strings. It specifies keyword arguments to |
| be added to the end of the the argument list. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{buffer}{object\optional{, offset\optional{, size}}} |
| The \var{object} argument must be an object that supports the |
| buffer call interface (such as strings, arrays, and buffers). A new |
| buffer object will be created which references the \var{object} argument. |
| The buffer object will be a slice from the beginning of \var{object} |
| (or from the specified \var{offset}). The slice will extend to the |
| end of \var{object} (or will have a length given by the \var{size} |
| argument). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{callable}{object} |
| Return true if the \var{object} argument appears callable, false if |
| not. If this returns true, it is still possible that a call fails, |
| but if it is false, calling \var{object} will never succeed. Note |
| that classes are callable (calling a class returns a new instance); |
| class instances are callable if they have a \method{__call__()} method. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{chr}{i} |
| Return a string of one character whose \ASCII{} code is the integer |
| \var{i}, e.g., \code{chr(97)} returns the string \code{'a'}. This is the |
| inverse of \function{ord()}. The argument must be in the range [0..255], |
| inclusive; \exception{ValueError} will be raised if \var{i} is |
| outside that range. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{cmp}{x, y} |
| Compare the two objects \var{x} and \var{y} and return an integer |
| according to the outcome. The return value is negative if \code{\var{x} |
| < \var{y}}, zero if \code{\var{x} == \var{y}} and strictly positive if |
| \code{\var{x} > \var{y}}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{coerce}{x, y} |
| Return a tuple consisting of the two numeric arguments converted to |
| a common type, using the same rules as used by arithmetic |
| operations. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{compile}{string, filename, kind} |
| Compile the \var{string} into a code object. Code objects can be |
| executed by an \keyword{exec} statement or evaluated by a call to |
| \function{eval()}. The \var{filename} argument should |
| give the file from which the code was read; pass e.g. \code{'<string>'} |
| if it wasn't read from a file. The \var{kind} argument specifies |
| what kind of code must be compiled; it can be \code{'exec'} if |
| \var{string} consists of a sequence of statements, \code{'eval'} |
| if it consists of a single expression, or \code{'single'} if |
| it consists of a single interactive statement (in the latter case, |
| expression statements that evaluate to something else than |
| \code{None} will printed). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{complex}{real\optional{, imag}} |
| Create a complex number with the value \var{real} + \var{imag}*j or |
| convert a string or number to a complex number. |
| Each argument may be any numeric type (including complex). |
| If \var{imag} is omitted, it defaults to zero and the function |
| serves as a numeric conversion function like \function{int()}, |
| \function{long()} and \function{float()}; in this case it also |
| accepts a string argument which should be a valid complex number. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{delattr}{object, name} |
| This is a relative of \function{setattr()}. The arguments are an |
| object and a string. The string must be the name |
| of one of the object's attributes. The function deletes |
| the named attribute, provided the object allows it. For example, |
| \code{delattr(\var{x}, '\var{foobar}')} is equivalent to |
| \code{del \var{x}.\var{foobar}}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{dir}{\optional{object}} |
| Without arguments, return the list of names in the current local |
| symbol table. With an argument, attempts to return a list of valid |
| attribute for that object. This information is gleaned from the |
| object's \member{__dict__}, \member{__methods__} and \member{__members__} |
| attributes, if defined. The list is not necessarily complete; e.g., |
| for classes, attributes defined in base classes are not included, |
| and for class instances, methods are not included. |
| The resulting list is sorted alphabetically. For example: |
| |
| \begin{verbatim} |
| >>> import sys |
| >>> dir() |
| ['sys'] |
| >>> dir(sys) |
| ['argv', 'exit', 'modules', 'path', 'stderr', 'stdin', 'stdout'] |
| \end{verbatim} |
| \end{funcdesc} |
| |
| \begin{funcdesc}{divmod}{a, b} |
| Take two numbers as arguments and return a pair of numbers consisting |
| of their quotient and remainder when using long division. With mixed |
| operand types, the rules for binary arithmetic operators apply. For |
| plain and long integers, the result is the same as |
| \code{(\var{a} / \var{b}, \var{a} \%{} \var{b})}. |
| For floating point numbers the result is \code{(\var{q}, \var{a} \%{} |
| \var{b})}, where \var{q} is usually \code{math.floor(\var{a} / |
| \var{b})} but may be 1 less than that. In any case \code{\var{q} * |
| \var{b} + \var{a} \%{} \var{b}} is very close to \var{a}, if |
| \code{\var{a} \%{} \var{b}} is non-zero it has the same sign as |
| \var{b}, and \code{0 <= abs(\var{a} \%{} \var{b}) < abs(\var{b})}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{eval}{expression\optional{, globals\optional{, locals}}} |
| The arguments are a string and two optional dictionaries. The |
| \var{expression} argument is parsed and evaluated as a Python |
| expression (technically speaking, a condition list) using the |
| \var{globals} and \var{locals} dictionaries as global and local name |
| space. If the \var{locals} dictionary is omitted it defaults to |
| the \var{globals} dictionary. If both dictionaries are omitted, the |
| expression is executed in the environment where \keyword{eval} is |
| called. The return value is the result of the evaluated expression. |
| Syntax errors are reported as exceptions. Example: |
| |
| \begin{verbatim} |
| >>> x = 1 |
| >>> print eval('x+1') |
| 2 |
| \end{verbatim} |
| |
| This function can also be used to execute arbitrary code objects |
| (e.g.\ created by \function{compile()}). In this case pass a code |
| object instead of a string. The code object must have been compiled |
| passing \code{'eval'} to the \var{kind} argument. |
| |
| Hints: dynamic execution of statements is supported by the |
| \keyword{exec} statement. Execution of statements from a file is |
| supported by the \function{execfile()} function. The |
| \function{globals()} and \function{locals()} functions returns the |
| current global and local dictionary, respectively, which may be |
| useful to pass around for use by \function{eval()} or |
| \function{execfile()}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{execfile}{file\optional{, globals\optional{, locals}}} |
| This function is similar to the |
| \keyword{exec} statement, but parses a file instead of a string. It |
| is different from the \keyword{import} statement in that it does not |
| use the module administration --- it reads the file unconditionally |
| and does not create a new module.\footnote{It is used relatively |
| rarely so does not warrant being made into a statement.} |
| |
| The arguments are a file name and two optional dictionaries. The |
| file is parsed and evaluated as a sequence of Python statements |
| (similarly to a module) using the \var{globals} and \var{locals} |
| dictionaries as global and local name space. If the \var{locals} |
| dictionary is omitted it defaults to the \var{globals} dictionary. |
| If both dictionaries are omitted, the expression is executed in the |
| environment where \function{execfile()} is called. The return value is |
| \code{None}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{filter}{function, list} |
| Construct a list from those elements of \var{list} for which |
| \var{function} returns true. If \var{list} is a string or a tuple, |
| the result also has that type; otherwise it is always a list. If |
| \var{function} is \code{None}, the identity function is assumed, |
| i.e.\ all elements of \var{list} that are false (zero or empty) are |
| removed. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{float}{x} |
| Convert a string or a number to floating point. If the argument is a |
| string, it must contain a possibly signed decimal or floating point |
| number, possibly embedded in whitespace; this behaves identical to |
| \code{string.atof(\var{x})}. Otherwise, the argument may be a plain |
| or long integer or a floating point number, and a floating point |
| number with the same value (within Python's floating point |
| precision) is returned. |
| |
| \strong{Note:} When passing in a string, values for NaN\index{NaN} |
| and Infinity\index{Infinity} may be returned, depending on the |
| underlying C library. The specific set of strings accepted which |
| cause these values to be returned depends entirely on the C library |
| and is known to vary. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{getattr}{object, name\optional{, default}} |
| Return the value of the named attributed of \var{object}. \var{name} |
| must be a string. If the string is the name of one of the object's |
| attributes, the result is the value of that attribute. For example, |
| \code{getattr(x, 'foobar')} is equivalent to \code{x.foobar}. If the |
| named attribute does not exist, \var{default} is returned if provided, |
| otherwise \exception{AttributeError} is raised. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{globals}{} |
| Return a dictionary representing the current global symbol table. |
| This is always the dictionary of the current module (inside a |
| function or method, this is the module where it is defined, not the |
| module from which it is called). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{hasattr}{object, name} |
| The arguments are an object and a string. The result is 1 if the |
| string is the name of one of the object's attributes, 0 if not. |
| (This is implemented by calling \code{getattr(\var{object}, |
| \var{name})} and seeing whether it raises an exception or not.) |
| \end{funcdesc} |
| |
| \begin{funcdesc}{hash}{object} |
| Return the hash value of the object (if it has one). Hash values |
| are integers. They are used to quickly compare dictionary |
| keys during a dictionary lookup. Numeric values that compare equal |
| have the same hash value (even if they are of different types, e.g. |
| 1 and 1.0). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{hex}{x} |
| Convert an integer number (of any size) to a hexadecimal string. |
| The result is a valid Python expression. Note: this always yields |
| an unsigned literal, e.g. on a 32-bit machine, \code{hex(-1)} yields |
| \code{'0xffffffff'}. When evaluated on a machine with the same |
| word size, this literal is evaluated as -1; at a different word |
| size, it may turn up as a large positive number or raise an |
| \exception{OverflowError} exception. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{id}{object} |
| Return the `identity' of an object. This is an integer (or long |
| integer) which is guaranteed to be unique and constant for this |
| object during its lifetime. Two objects whose lifetimes are |
| disjunct may have the same \function{id()} value. (Implementation |
| note: this is the address of the object.) |
| \end{funcdesc} |
| |
| \begin{funcdesc}{input}{\optional{prompt}} |
| Equivalent to \code{eval(raw_input(\var{prompt}))}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{int}{x\optional{, radix}} |
| Convert a string or number to a plain integer. If the argument is a |
| string, it must contain a possibly signed decimal number |
| representable as a Python integer, possibly embedded in whitespace; |
| this behaves identical to \code{string.atoi(\var{x}\optional{, |
| \var{radix}})}. The \var{radix} parameter gives the base for the |
| conversion and may be any integer in the range [2, 36]. If |
| \var{radix} is specified and \var{x} is not a string, |
| \exception{TypeError} is raised. |
| Otherwise, the argument may be a plain or |
| long integer or a floating point number. Conversion of floating |
| point numbers to integers is defined by the C semantics; normally |
| the conversion truncates towards zero.\footnote{This is ugly --- the |
| language definition should require truncation towards zero.} |
| \end{funcdesc} |
| |
| \begin{funcdesc}{intern}{string} |
| Enter \var{string} in the table of ``interned'' strings and return |
| the interned string -- which is \var{string} itself or a copy. |
| Interning strings is useful to gain a little performance on |
| dictionary lookup -- if the keys in a dictionary are interned, and |
| the lookup key is interned, the key comparisons (after hashing) can |
| be done by a pointer compare instead of a string compare. Normally, |
| the names used in Python programs are automatically interned, and |
| the dictionaries used to hold module, class or instance attributes |
| have interned keys. Interned strings are immortal (i.e. never get |
| garbage collected). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{isinstance}{object, class} |
| Return true if the \var{object} argument is an instance of the |
| \var{class} argument, or of a (direct or indirect) subclass thereof. |
| Also return true if \var{class} is a type object and \var{object} is |
| an object of that type. If \var{object} is not a class instance or a |
| object of the given type, the function always returns false. If |
| \var{class} is neither a class object nor a type object, a |
| \exception{TypeError} exception is raised. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{issubclass}{class1, class2} |
| Return true if \var{class1} is a subclass (direct or indirect) of |
| \var{class2}. A class is considered a subclass of itself. If either |
| argument is not a class object, a \exception{TypeError} exception is |
| raised. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{len}{s} |
| Return the length (the number of items) of an object. The argument |
| may be a sequence (string, tuple or list) or a mapping (dictionary). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{list}{sequence} |
| Return a list whose items are the same and in the same order as |
| \var{sequence}'s items. If \var{sequence} is already a list, |
| a copy is made and returned, similar to \code{\var{sequence}[:]}. |
| For instance, \code{list('abc')} returns |
| returns \code{['a', 'b', 'c']} and \code{list( (1, 2, 3) )} returns |
| \code{[1, 2, 3]}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{locals}{} |
| Return a dictionary representing the current local symbol table. |
| \strong{Warning:} the contents of this dictionary should not be |
| modified; changes may not affect the values of local variables used by |
| the interpreter. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{long}{x} |
| Convert a string or number to a long integer. If the argument is a |
| string, it must contain a possibly signed decimal number of |
| arbitrary size, possibly embedded in whitespace; |
| this behaves identical to \code{string.atol(\var{x})}. |
| Otherwise, the argument may be a plain or |
| long integer or a floating point number, and a long integer with |
| the same value is returned. Conversion of floating |
| point numbers to integers is defined by the C semantics; |
| see the description of \function{int()}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{map}{function, list, ...} |
| Apply \var{function} to every item of \var{list} and return a list |
| of the results. If additional \var{list} arguments are passed, |
| \var{function} must take that many arguments and is applied to |
| the items of all lists in parallel; if a list is shorter than another |
| it is assumed to be extended with \code{None} items. If |
| \var{function} is \code{None}, the identity function is assumed; if |
| there are multiple list arguments, \function{map()} returns a list |
| consisting of tuples containing the corresponding items from all lists |
| (i.e. a kind of transpose operation). The \var{list} arguments may be |
| any kind of sequence; the result is always a list. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{max}{s\optional{, args...}} |
| With a single argument \var{s}, return the largest item of a |
| non-empty sequence (e.g., a string, tuple or list). With more than |
| one argument, return the largest of the arguments. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{min}{s\optional{, args...}} |
| With a single argument \var{s}, return the smallest item of a |
| non-empty sequence (e.g., a string, tuple or list). With more than |
| one argument, return the smallest of the arguments. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{oct}{x} |
| Convert an integer number (of any size) to an octal string. The |
| result is a valid Python expression. Note: this always yields |
| an unsigned literal, e.g. on a 32-bit machine, \code{oct(-1)} yields |
| \code{'037777777777'}. When evaluated on a machine with the same |
| word size, this literal is evaluated as -1; at a different word |
| size, it may turn up as a large positive number or raise an |
| \exception{OverflowError} exception. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{open}{filename\optional{, mode\optional{, bufsize}}} |
| Return a new file object (described earlier under Built-in Types). |
| The first two arguments are the same as for \code{stdio}'s |
| \cfunction{fopen()}: \var{filename} is the file name to be opened, |
| \var{mode} indicates how the file is to be opened: \code{'r'} for |
| reading, \code{'w'} for writing (truncating an existing file), and |
| \code{'a'} opens it for appending (which on \emph{some} \UNIX{} |
| systems means that \emph{all} writes append to the end of the file, |
| regardless of the current seek position). |
| |
| Modes \code{'r+'}, \code{'w+'} and \code{'a+'} open the file for |
| updating (note that \code{'w+'} truncates the file). Append |
| \code{'b'} to the mode to open the file in binary mode, on systems |
| that differentiate between binary and text files (else it is |
| ignored). If the file cannot be opened, \exception{IOError} is |
| raised. |
| |
| If \var{mode} is omitted, it defaults to \code{'r'}. When opening a |
| binary file, you should append \code{'b'} to the \var{mode} value |
| for improved portability. (It's useful even on systems which don't |
| treat binary and text files differently, where it serves as |
| documentation.) |
| \index{line-buffered I/O}\index{unbuffered I/O}\index{buffer size, I/O} |
| \index{I/O control!buffering} |
| The optional \var{bufsize} argument specifies the |
| file's desired buffer size: 0 means unbuffered, 1 means line |
| buffered, any other positive value means use a buffer of |
| (approximately) that size. A negative \var{bufsize} means to use |
| the system default, which is usually line buffered for for tty |
| devices and fully buffered for other files. If omitted, the system |
| default is used.\footnote{ |
| Specifying a buffer size currently has no effect on systems that |
| don't have \cfunction{setvbuf()}. The interface to specify the |
| buffer size is not done using a method that calls |
| \cfunction{setvbuf()}, because that may dump core when called |
| after any I/O has been performed, and there's no reliable way to |
| determine whether this is the case.} |
| \end{funcdesc} |
| |
| \begin{funcdesc}{ord}{c} |
| Return the \ASCII{} value of a string of one character or a Unicode |
| character. E.g., \code{ord('a')} returns the integer \code{97}, |
| \code{ord(u'\\u2020')} returns \code{8224}. This is the inverse of |
| \function{chr()} for strings and of \function{unichr()} for Unicode |
| characters. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{pow}{x, y\optional{, z}} |
| Return \var{x} to the power \var{y}; if \var{z} is present, return |
| \var{x} to the power \var{y}, modulo \var{z} (computed more |
| efficiently than \code{pow(\var{x}, \var{y}) \%\ \var{z}}). |
| The arguments must have |
| numeric types. With mixed operand types, the rules for binary |
| arithmetic operators apply. The effective operand type is also the |
| type of the result; if the result is not expressible in this type, the |
| function raises an exception; e.g., \code{pow(2, -1)} or \code{pow(2, |
| 35000)} is not allowed. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{range}{\optional{start,} stop\optional{, step}} |
| This is a versatile function to create lists containing arithmetic |
| progressions. It is most often used in \keyword{for} loops. The |
| arguments must be plain integers. If the \var{step} argument is |
| omitted, it defaults to \code{1}. If the \var{start} argument is |
| omitted, it defaults to \code{0}. The full form returns a list of |
| plain integers \code{[\var{start}, \var{start} + \var{step}, |
| \var{start} + 2 * \var{step}, \ldots]}. If \var{step} is positive, |
| the last element is the largest \code{\var{start} + \var{i} * |
| \var{step}} less than \var{stop}; if \var{step} is negative, the last |
| element is the largest \code{\var{start} + \var{i} * \var{step}} |
| greater than \var{stop}. \var{step} must not be zero (or else |
| \exception{ValueError} is raised). Example: |
| |
| \begin{verbatim} |
| >>> range(10) |
| [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] |
| >>> range(1, 11) |
| [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] |
| >>> range(0, 30, 5) |
| [0, 5, 10, 15, 20, 25] |
| >>> range(0, 10, 3) |
| [0, 3, 6, 9] |
| >>> range(0, -10, -1) |
| [0, -1, -2, -3, -4, -5, -6, -7, -8, -9] |
| >>> range(0) |
| [] |
| >>> range(1, 0) |
| [] |
| \end{verbatim} |
| \end{funcdesc} |
| |
| \begin{funcdesc}{raw_input}{\optional{prompt}} |
| If the \var{prompt} argument is present, it is written to standard output |
| without a trailing newline. The function then reads a line from input, |
| converts it to a string (stripping a trailing newline), and returns that. |
| When \EOF{} is read, \exception{EOFError} is raised. Example: |
| |
| \begin{verbatim} |
| >>> s = raw_input('--> ') |
| --> Monty Python's Flying Circus |
| >>> s |
| "Monty Python's Flying Circus" |
| \end{verbatim} |
| |
| If the \module{readline} module was loaded, then |
| \function{raw_input()} will use it to provide elaborate |
| line editing and history features. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{reduce}{function, sequence\optional{, initializer}} |
| Apply \var{function} of two arguments cumulatively to the items of |
| \var{sequence}, from left to right, so as to reduce the sequence to |
| a single value. For example, |
| \code{reduce(lambda x, y: x+y, [1, 2, 3, 4, 5])} calculates |
| \code{((((1+2)+3)+4)+5)}. |
| If the optional \var{initializer} is present, it is placed before the |
| items of the sequence in the calculation, and serves as a default when |
| the sequence is empty. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{reload}{module} |
| Re-parse and re-initialize an already imported \var{module}. The |
| argument must be a module object, so it must have been successfully |
| imported before. This is useful if you have edited the module source |
| file using an external editor and want to try out the new version |
| without leaving the Python interpreter. The return value is the |
| module object (i.e.\ the same as the \var{module} argument). |
| |
| There are a number of caveats: |
| |
| If a module is syntactically correct but its initialization fails, the |
| first \keyword{import} statement for it does not bind its name locally, |
| but does store a (partially initialized) module object in |
| \code{sys.modules}. To reload the module you must first |
| \keyword{import} it again (this will bind the name to the partially |
| initialized module object) before you can \function{reload()} it. |
| |
| When a module is reloaded, its dictionary (containing the module's |
| global variables) is retained. Redefinitions of names will override |
| the old definitions, so this is generally not a problem. If the new |
| version of a module does not define a name that was defined by the old |
| version, the old definition remains. This feature can be used to the |
| module's advantage if it maintains a global table or cache of objects |
| --- with a \keyword{try} statement it can test for the table's presence |
| and skip its initialization if desired. |
| |
| It is legal though generally not very useful to reload built-in or |
| dynamically loaded modules, except for \module{sys}, \module{__main__} |
| and \module{__builtin__}. In certain cases, however, extension |
| modules are not designed to be initialized more than once, and may |
| fail in arbitrary ways when reloaded. |
| |
| If a module imports objects from another module using \keyword{from} |
| \ldots{} \keyword{import} \ldots{}, calling \function{reload()} for |
| the other module does not redefine the objects imported from it --- |
| one way around this is to re-execute the \keyword{from} statement, |
| another is to use \keyword{import} and qualified names |
| (\var{module}.\var{name}) instead. |
| |
| If a module instantiates instances of a class, reloading the module |
| that defines the class does not affect the method definitions of the |
| instances --- they continue to use the old class definition. The same |
| is true for derived classes. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{repr}{object} |
| Return a string containing a printable representation of an object. |
| This is the same value yielded by conversions (reverse quotes). |
| It is sometimes useful to be able to access this operation as an |
| ordinary function. For many types, this function makes an attempt |
| to return a string that would yield an object with the same value |
| when passed to \function{eval()}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{round}{x\optional{, n}} |
| Return the floating point value \var{x} rounded to \var{n} digits |
| after the decimal point. If \var{n} is omitted, it defaults to zero. |
| The result is a floating point number. Values are rounded to the |
| closest multiple of 10 to the power minus \var{n}; if two multiples |
| are equally close, rounding is done away from 0 (so e.g. |
| \code{round(0.5)} is \code{1.0} and \code{round(-0.5)} is \code{-1.0}). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{setattr}{object, name, value} |
| This is the counterpart of \function{getattr()}. The arguments are an |
| object, a string and an arbitrary value. The string may name an |
| existing attribute or a new attribute. The function assigns the |
| value to the attribute, provided the object allows it. For example, |
| \code{setattr(\var{x}, '\var{foobar}', 123)} is equivalent to |
| \code{\var{x}.\var{foobar} = 123}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{slice}{\optional{start,} stop\optional{, step}} |
| Return a slice object representing the set of indices specified by |
| \code{range(\var{start}, \var{stop}, \var{step})}. The \var{start} |
| and \var{step} arguments default to None. Slice objects have |
| read-only data attributes \member{start}, \member{stop} and \member{step} |
| which merely return the argument values (or their default). They have |
| no other explicit functionality; however they are used by Numerical |
| Python\index{Numerical Python} and other third party extensions. |
| Slice objects are also generated when extended indexing syntax is |
| used, e.g. for \samp{a[start:stop:step]} or \samp{a[start:stop, i]}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{str}{object} |
| Return a string containing a nicely printable representation of an |
| object. For strings, this returns the string itself. The difference |
| with \code{repr(\var{object})} is that \code{str(\var{object})} does not |
| always attempt to return a string that is acceptable to \function{eval()}; |
| its goal is to return a printable string. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{tuple}{sequence} |
| Return a tuple whose items are the same and in the same order as |
| \var{sequence}'s items. If \var{sequence} is already a tuple, it |
| is returned unchanged. For instance, \code{tuple('abc')} returns |
| returns \code{('a', 'b', 'c')} and \code{tuple([1, 2, 3])} returns |
| \code{(1, 2, 3)}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{type}{object} |
| Return the type of an \var{object}. The return value is a type |
| object. The standard module \module{types} defines names for all |
| built-in types. |
| \refstmodindex{types} |
| \obindex{type} |
| For instance: |
| |
| \begin{verbatim} |
| >>> import types |
| >>> if type(x) == types.StringType: print "It's a string" |
| \end{verbatim} |
| \end{funcdesc} |
| |
| \begin{funcdesc}{unichr}{i} |
| Return the Unicode string of one character whose Unicode code is the |
| integer \var{i}, e.g., \code{unichr(97)} returns the string |
| \code{u'a'}. This is the inverse of \function{ord()} for Unicode |
| strings. The argument must be in the range [0..65535], inclusive. |
| \exception{ValueError} is raised otherwise. |
| \versionadded{2.0} |
| \end{funcdesc} |
| |
| \begin{funcdesc}{unicode}{string\optional{, encoding='utf-8'\optional{, errors='strict'}}} |
| Decodes \var{string} using the codec for \var{encoding}. Error |
| handling is done according to \var{errors}. The default behavior is |
| to decode UTF-8 in strict mode, meaning that encoding errors raise |
| \exception{ValueError}. |
| \versionadded{2.0} |
| \end{funcdesc} |
| |
| \begin{funcdesc}{vars}{\optional{object}} |
| Without arguments, return a dictionary corresponding to the current |
| local symbol table. With a module, class or class instance object as |
| argument (or anything else that has a \member{__dict__} attribute), |
| returns a dictionary corresponding to the object's symbol table. |
| The returned dictionary should not be modified: the effects on the |
| corresponding symbol table are undefined.\footnote{ |
| In the current implementation, local variable bindings cannot |
| normally be affected this way, but variables retrieved from |
| other scopes (e.g. modules) can be. This may change.} |
| \end{funcdesc} |
| |
| \begin{funcdesc}{xrange}{\optional{start,} stop\optional{, step}} |
| This function is very similar to \function{range()}, but returns an |
| ``xrange object'' instead of a list. This is an opaque sequence type |
| which yields the same values as the corresponding list, without |
| actually storing them all simultaneously. The advantage of |
| \function{xrange()} over \function{range()} is minimal (since |
| \function{xrange()} still has to create the values when asked for |
| them) except when a very large range is used on a memory-starved |
| machine (e.g. MS-DOS) or when all of the range's elements are never |
| used (e.g. when the loop is usually terminated with \keyword{break}). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{zip}{seq1, \moreargs} |
| This function returns a list of tuples, where each tuple contains the |
| \var{i}-th element from each of the argument sequences. At least one |
| sequence is required, otherwise a \exception{TypeError} is raised. |
| The returned list is truncated in length to the length of the shortest |
| argument sequence. When the argument sequences are all of the same |
| length, \function{zip()} is similar to \function{map()} with an |
| initial argument of \code{None}. |
| \versionadded{2.0} |
| \end{funcdesc} |