| \section{Built-in Functions} |
| |
| The Python interpreter has a number of functions built into it that |
| are always available. They are listed here in alphabetical order. |
| |
| |
| \renewcommand{\indexsubitem}{(built-in function)} |
| \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. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{apply}{function\, args} |
| 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 tuple. The \var{function} is called with |
| \var{args} as 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.) |
| \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 \code{ord()}. The argument must be in the range [0..255], |
| inclusive. |
| \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 a \code{exec()} statement or evaluated by a call to |
| \code{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, or \code{'eval'} |
| if it consists of a single expression. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{dir}{} |
| Without arguments, return the list of names in the current local |
| symbol table. With a module, class or class instance object as |
| argument (or anything else that has a \code{__dict__} attribute), |
| returns the list of names in that object's attribute dictionary. |
| The resulting list is sorted. For example: |
| |
| \bcode\begin{verbatim} |
| >>> import sys |
| >>> dir() |
| ['sys'] |
| >>> dir(sys) |
| ['argv', 'exit', 'modules', 'path', 'stderr', 'stdin', 'stdout'] |
| >>> |
| \end{verbatim}\ecode |
| \end{funcdesc} |
| |
| \begin{funcdesc}{divmod}{a\, b} |
| Take two numbers as arguments and return a pair of integers |
| consisting of their integer quotient and remainder. 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 the same as |
| \code{(math.floor(\var{a} / \var{b}), \var{a} \%{} \var{b})}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{eval}{s\optional{\, globals\optional{\, locals}}} |
| The arguments are a string and two optional dictionaries. The |
| string argument is parsed and evaluated as a Python expression |
| (technically speaking, a condition list) using the dictionaries as |
| global and local name space. The string must not contain null bytes |
| or newline characters. The return value is the |
| result of the expression. If the third argument is omitted it |
| defaults to the second. If both dictionaries are omitted, the |
| expression is executed in the environment where \code{eval} is |
| called. Syntax errors are reported as exceptions. Example: |
| |
| \bcode\begin{verbatim} |
| >>> x = 1 |
| >>> print eval('x+1') |
| 2 |
| >>> |
| \end{verbatim}\ecode |
| |
| This function can also be used to execute arbitrary code objects |
| (e.g. created by \code{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. |
| |
| Note: dynamic execution of statements is supported by the |
| \code{exec} statement. |
| |
| \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 number to floating point. The argument may be a plain or |
| long integer or a floating point number. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{getattr}{object\, name} |
| The arguments are an object and a string. The string must be the |
| name |
| of one of the object's attributes. The result is the value of that |
| attribute. For example, \code{getattr(\var{x}, '\var{foobar}')} is equivalent to |
| \code{\var{x}.\var{foobar}}. |
| \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(object, 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 32-bit 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 a number to a hexadecimal string. The result is a valid |
| Python expression. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{id}{object} |
| Return the `identity' of an object. This is an 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 id() value.) (Implementation note: this is the address of the |
| object.) |
| \end{funcdesc} |
| |
| \begin{funcdesc}{input}{\optional{prompt}} |
| Almost equivalent to \code{eval(raw_input(\var{prompt}))}. Like |
| \code{raw_input()}, the \var{prompt} argument is optional. The difference |
| is that a long input expression may be broken over multiple lines using |
| the backslash convention. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{int}{x} |
| Convert a number to a plain integer. The argument may be a plain or |
| long integer or a floating point number. |
| \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}{long}{x} |
| Convert a number to a long integer. The argument may be a plain or |
| long integer or a floating point number. |
| \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, \code{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} |
| Return the largest item of a non-empty sequence (string, tuple or |
| list). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{min}{s} |
| Return the smallest item of a non-empty sequence (string, tuple or |
| list). |
| \end{funcdesc} |
| |
| \begin{funcdesc}{oct}{x} |
| Convert a number to an octal string. The result is a valid Python |
| expression. |
| \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 |
| \code{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. Modes \code{'r+'}, \code{'w+'} and |
| \code{'a+'} open the file for updating, provided the underlying |
| \code{stdio} library understands this. On systems that differentiate |
| between binary and text files, \code{'b'} appended to the mode opens |
| the file in binary mode. If the file cannot be opened, \code{IOError} |
| is raised. |
| If \var{mode} is omitted, it defaults to \code{'r'}. |
| 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.% |
| \footnote{Specifying a buffer size currently has no effect on systems |
| that don't have \code{setvbuf()}. The interface to specify the buffer |
| size is not done using a method that calls \code{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. E.g., |
| \code{ord('a')} returns the integer \code{97}. This is the inverse of |
| \code{chr()}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{pow}{x\, y\optional{\, z}} |
| Return \var{x} to the power \var{y}; if \var{z} is present, $x^y \bmod z$ |
| is returned. 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\,} end\optional{\, step}} |
| This is a versatile function to create lists containing arithmetic |
| progressions. It is most often used in \code{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{end}; if \var{step} is negative, the last |
| element is the largest \code{\var{start} + \var{i} * \var{step}} |
| greater than \var{end}. \var{step} must not be zero. Example: |
| |
| \bcode\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}\ecode |
| \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, \code{EOFError} is raised. Example: |
| |
| \bcode\begin{verbatim} |
| >>> s = raw_input('--> ') |
| --> Monty Python's Flying Circus |
| >>> s |
| 'Monty Python\'s Flying Circus' |
| >>> |
| \end{verbatim}\ecode |
| \end{funcdesc} |
| |
| \begin{funcdesc}{reduce}{function\, list\optional{\, initializer}} |
| Apply the binary \var{function} to the items of \var{list} so as to |
| reduce the list to a single value. E.g., |
| \code{reduce(lambda x, y: x*y, \var{list}, 1)} returns the product of |
| the elements of \var{list}. The optional \var{initializer} can be |
| thought of as being prepended to \var{list} so as to allow reduction |
| of an empty \var{list}. The \var{list} arguments may be any kind of |
| sequence. |
| \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. Note that if a module is |
| syntactically correct but its initialization fails, the first |
| \code{import} statement for it does not import the name, but does |
| create a (partially initialized) module object; to reload the module |
| you must first \code{import} it again (this will just make the |
| partially initialized module object available) before you can |
| \code{reload()} it. |
| \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 \code{eval()}. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{round}{x\, 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 \code{getattr}. The arguments are an |
| object, a string and an arbitrary value. The string must be the name |
| of one of the object's attributes. 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}{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 \code{eval()}; |
| its goal is to return a printable string. |
| \end{funcdesc} |
| |
| \begin{funcdesc}{type}{object} |
| % XXXJH xref to buil-in objects here? |
| Return the type of an \var{object}. The return value is a type |
| object. There is not much you can do with type objects except compare |
| them to other type objects; e.g., the following checks if a variable |
| is a string: |
| |
| \bcode\begin{verbatim} |
| >>> if type(x) == type(''): print 'It is a string' |
| \end{verbatim}\ecode |
| \end{funcdesc} |
| |
| \begin{funcdesc}{vars}{} |
| 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 \code{__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 can be. This may change.} |
| \end{funcdesc} |
| |
| \begin{funcdesc}{xrange}{\optional{start\,} end\optional{\, step}} |
| This function is very similar to \code{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 |
| \code{xrange()} over \code{range()} is minimal (since \code{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. DOS) or when all |
| of the range's elements are never used (e.g. when the loop is usually |
| terminated with \code{break}). |
| \end{funcdesc} |