mirror of https://github.com/python/cpython.git
392 lines
16 KiB
TeX
392 lines
16 KiB
TeX
\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\, globals\, 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}{prompt}
|
|
Almost equivalent to \code{eval(raw_input(\var{prompt}))}. As for
|
|
\code{raw_input()}, the 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\, mode\, 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}
|
|
Return \var{x} to the power \var{y}. 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)} is not allowed.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{range}{start\, end\, 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}{prompt}
|
|
The string argument is optional; if 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\, 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}{start\, end\, 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}
|