805 lines
38 KiB
TeX
805 lines
38 KiB
TeX
\section{Built-in Functions \label{built-in-funcs}}
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The Python interpreter has a number of functions built into it that
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are always available. They are listed here in alphabetical order.
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\setindexsubitem{(built-in function)}
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\begin{funcdesc}{__import__}{name\optional{, globals\optional{, locals\optional{, fromlist}}}}
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This function is invoked by the
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\keyword{import}\stindex{import} statement. It mainly
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exists so that you can replace it with another function that has a
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compatible interface, in order to change the semantics of the
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\keyword{import} statement. For examples of why and how you would do
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this, see the standard library modules
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\module{ihooks}\refstmodindex{ihooks} and
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\refmodule{rexec}\refstmodindex{rexec}. See also the built-in module
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\refmodule{imp}\refbimodindex{imp}, which defines some useful
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operations out of which you can build your own
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\function{__import__()} function.
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For example, the statement \samp{import spam} results in the
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following call:
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\code{__import__('spam',} \code{globals(),} \code{locals(), [])};
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the statement \samp{from spam.ham import eggs} results
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in \samp{__import__('spam.ham', globals(), locals(), ['eggs'])}.
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Note that even though \code{locals()} and \code{['eggs']} are passed
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in as arguments, the \function{__import__()} function does not set the
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local variable named \code{eggs}; this is done by subsequent code that
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is generated for the import statement. (In fact, the standard
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implementation does not use its \var{locals} argument at all, and uses
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its \var{globals} only to determine the package context of the
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\keyword{import} statement.)
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When the \var{name} variable is of the form \code{package.module},
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normally, the top-level package (the name up till the first dot) is
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returned, \emph{not} the module named by \var{name}. However, when a
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non-empty \var{fromlist} argument is given, the module named by
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\var{name} is returned. This is done for compatibility with the
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bytecode generated for the different kinds of import statement; when
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using \samp{import spam.ham.eggs}, the top-level package \code{spam}
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must be placed in the importing namespace, but when using \samp{from
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spam.ham import eggs}, the \code{spam.ham} subpackage must be used to
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find the \code{eggs} variable.
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As a workaround for this behavior, use \function{getattr()} to extract
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the desired components. For example, you could define the following
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helper:
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\begin{verbatim}
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import string
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def my_import(name):
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mod = __import__(name)
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components = string.split(name, '.')
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for comp in components[1:]:
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mod = getattr(mod, comp)
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return mod
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\end{verbatim}
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\end{funcdesc}
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\begin{funcdesc}{abs}{x}
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Return the absolute value of a number. The argument may be a plain
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or long integer or a floating point number. If the argument is a
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complex number, its magnitude is returned.
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\end{funcdesc}
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\begin{funcdesc}{apply}{function, args\optional{, keywords}}
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The \var{function} argument must be a callable object (a user-defined or
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built-in function or method, or a class object) and the \var{args}
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argument must be a sequence (if it is not a tuple, the sequence is
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first converted to a tuple). The \var{function} is called with
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\var{args} as the argument list; the number of arguments is the the length
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of the tuple. (This is different from just calling
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\code{\var{func}(\var{args})}, since in that case there is always
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exactly one argument.)
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If the optional \var{keywords} argument is present, it must be a
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dictionary whose keys are strings. It specifies keyword arguments to
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be added to the end of the the argument list.
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\end{funcdesc}
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\begin{funcdesc}{buffer}{object\optional{, offset\optional{, size}}}
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The \var{object} argument must be an object that supports the
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buffer call interface (such as strings, arrays, and buffers). A new
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buffer object will be created which references the \var{object} argument.
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The buffer object will be a slice from the beginning of \var{object}
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(or from the specified \var{offset}). The slice will extend to the
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end of \var{object} (or will have a length given by the \var{size}
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argument).
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\end{funcdesc}
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\begin{funcdesc}{callable}{object}
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Return true if the \var{object} argument appears callable, false if
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not. If this returns true, it is still possible that a call fails,
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but if it is false, calling \var{object} will never succeed. Note
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that classes are callable (calling a class returns a new instance);
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class instances are callable if they have a \method{__call__()} method.
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\end{funcdesc}
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\begin{funcdesc}{chr}{i}
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Return a string of one character whose \ASCII{} code is the integer
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\var{i}. For example, \code{chr(97)} returns the string \code{'a'}.
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This is the inverse of \function{ord()}. The argument must be in
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the range [0..255], inclusive; \exception{ValueError} will be raised
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if \var{i} is outside that range.
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\end{funcdesc}
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\begin{funcdesc}{cmp}{x, y}
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Compare the two objects \var{x} and \var{y} and return an integer
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according to the outcome. The return value is negative if \code{\var{x}
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< \var{y}}, zero if \code{\var{x} == \var{y}} and strictly positive if
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\code{\var{x} > \var{y}}.
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\end{funcdesc}
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\begin{funcdesc}{coerce}{x, y}
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Return a tuple consisting of the two numeric arguments converted to
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a common type, using the same rules as used by arithmetic
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operations.
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\end{funcdesc}
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\begin{funcdesc}{compile}{string, filename, kind\optional{,
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flags\optional{, dont_inherit}}}
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Compile the \var{string} into a code object. Code objects can be
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executed by an \keyword{exec} statement or evaluated by a call to
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\function{eval()}. The \var{filename} argument should
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give the file from which the code was read; pass some recognizable value
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if it wasn't read from a file (\code{'<string>'} is commonly used).
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The \var{kind} argument specifies what kind of code must be
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compiled; it can be \code{'exec'} if \var{string} consists of a
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sequence of statements, \code{'eval'} if it consists of a single
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expression, or \code{'single'} if it consists of a single
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interactive statement (in the latter case, expression statements
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that evaluate to something else than \code{None} will printed).
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When compiling multi-line statements, two caveats apply: line
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endings must be represented by a single newline character
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(\code{'\e n'}), and the input must be terminated by at least one
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newline character. If line endings are represented by
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\code{'\e r\e n'}, use the string \method{replace()} method to
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change them into \code{'\e n'}.
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The optional arguments \var{flags} and \var{dont_inherit}
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(which are new in Python 2.2) control which future statements (see
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\pep{236}) affect the compilation of \var{string}. If neither is
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present (or both are zero) the code is compiled with those future
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statements that are in effect in the code that is calling compile.
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If the \var{flags} argument is given and \var{dont_inherit} is not
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(or is zero) then the future statements specified by the \var{flags}
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argument are used in addition to those that would be used anyway.
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If \var{dont_inherit} is a non-zero integer then the \var{flags}
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argument is it -- the future statements in effect around the call to
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compile are ignored.
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Future statemants are specified by bits which can be bitwise or-ed
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together to specify multiple statements. The bitfield required to
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specify a given feature can be found as the \member{compiler_flag}
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attribute on the \class{_Feature} instance in the
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\module{__future__} module.
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\end{funcdesc}
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\begin{funcdesc}{complex}{real\optional{, imag}}
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Create a complex number with the value \var{real} + \var{imag}*j or
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convert a string or number to a complex number.
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Each argument may be any numeric type (including complex).
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If \var{imag} is omitted, it defaults to zero and the function
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serves as a numeric conversion function like \function{int()},
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\function{long()} and \function{float()}; in this case it also
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accepts a string argument which should be a valid complex number.
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\end{funcdesc}
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\begin{funcdesc}{delattr}{object, name}
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This is a relative of \function{setattr()}. The arguments are an
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object and a string. The string must be the name
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of one of the object's attributes. The function deletes
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the named attribute, provided the object allows it. For example,
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\code{delattr(\var{x}, '\var{foobar}')} is equivalent to
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\code{del \var{x}.\var{foobar}}.
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\end{funcdesc}
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\begin{funcdesc}{dir}{\optional{object}}
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Without arguments, return the list of names in the current local
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symbol table. With an argument, attempts to return a list of valid
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attribute for that object. This information is gleaned from the
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object's \member{__dict__}, \member{__methods__} and \member{__members__}
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attributes, if defined. The list is not necessarily complete. For
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example, for classes, attributes defined in base classes are not
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included, and for class instances, methods are not included.
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The resulting list is sorted alphabetically. For example:
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\begin{verbatim}
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>>> import sys
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>>> dir()
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['sys']
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>>> dir(sys)
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['argv', 'exit', 'modules', 'path', 'stderr', 'stdin', 'stdout']
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\end{verbatim}
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\end{funcdesc}
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\begin{funcdesc}{divmod}{a, b}
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Take two numbers as arguments and return a pair of numbers consisting
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of their quotient and remainder when using long division. With mixed
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operand types, the rules for binary arithmetic operators apply. For
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plain and long integers, the result is the same as
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\code{(\var{a} / \var{b}, \var{a} \%{} \var{b})}.
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For floating point numbers the result is \code{(\var{q}, \var{a} \%{}
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\var{b})}, where \var{q} is usually \code{math.floor(\var{a} /
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\var{b})} but may be 1 less than that. In any case \code{\var{q} *
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\var{b} + \var{a} \%{} \var{b}} is very close to \var{a}, if
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\code{\var{a} \%{} \var{b}} is non-zero it has the same sign as
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\var{b}, and \code{0 <= abs(\var{a} \%{} \var{b}) < abs(\var{b})}.
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\end{funcdesc}
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\begin{funcdesc}{eval}{expression\optional{, globals\optional{, locals}}}
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The arguments are a string and two optional dictionaries. The
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\var{expression} argument is parsed and evaluated as a Python
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expression (technically speaking, a condition list) using the
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\var{globals} and \var{locals} dictionaries as global and local name
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space. If the \var{locals} dictionary is omitted it defaults to
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the \var{globals} dictionary. If both dictionaries are omitted, the
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expression is executed in the environment where \keyword{eval} is
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called. The return value is the result of the evaluated expression.
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Syntax errors are reported as exceptions. Example:
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\begin{verbatim}
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>>> x = 1
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>>> print eval('x+1')
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2
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\end{verbatim}
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This function can also be used to execute arbitrary code objects
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(such as those created by \function{compile()}). In this case pass
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a code object instead of a string. The code object must have been
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compiled passing \code{'eval'} as the \var{kind} argument.
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Hints: dynamic execution of statements is supported by the
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\keyword{exec} statement. Execution of statements from a file is
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supported by the \function{execfile()} function. The
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\function{globals()} and \function{locals()} functions returns the
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current global and local dictionary, respectively, which may be
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useful to pass around for use by \function{eval()} or
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\function{execfile()}.
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\end{funcdesc}
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\begin{funcdesc}{execfile}{file\optional{, globals\optional{, locals}}}
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This function is similar to the
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\keyword{exec} statement, but parses a file instead of a string. It
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is different from the \keyword{import} statement in that it does not
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use the module administration --- it reads the file unconditionally
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and does not create a new module.\footnote{It is used relatively
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rarely so does not warrant being made into a statement.}
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The arguments are a file name and two optional dictionaries. The
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file is parsed and evaluated as a sequence of Python statements
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(similarly to a module) using the \var{globals} and \var{locals}
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dictionaries as global and local namespace. If the \var{locals}
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dictionary is omitted it defaults to the \var{globals} dictionary.
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If both dictionaries are omitted, the expression is executed in the
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environment where \function{execfile()} is called. The return value is
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\code{None}.
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\strong{Warning:} The default \var{locals} act as described for function
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\function{locals()} below: modifications to the default \var{locals}
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dictionary should not be attempted. Pass an explicit \var{locals}
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dictionary if you need to see effects of the code on \var{locals} after
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function \function{execfile()} returns. \function{execfile()} cannot
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be used reliably to modify a function's locals.
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\end{funcdesc}
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\begin{funcdesc}{file}{filename\optional{, mode\optional{, bufsize}}}
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Return a new file object (described earlier under Built-in Types).
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The first two arguments are the same as for \code{stdio}'s
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\cfunction{fopen()}: \var{filename} is the file name to be opened,
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\var{mode} indicates how the file is to be opened: \code{'r'} for
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reading, \code{'w'} for writing (truncating an existing file), and
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\code{'a'} opens it for appending (which on \emph{some} \UNIX{}
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systems means that \emph{all} writes append to the end of the file,
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regardless of the current seek position).
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Modes \code{'r+'}, \code{'w+'} and \code{'a+'} open the file for
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updating (note that \code{'w+'} truncates the file). Append
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\code{'b'} to the mode to open the file in binary mode, on systems
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that differentiate between binary and text files (else it is
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ignored). If the file cannot be opened, \exception{IOError} is
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raised.
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If \var{mode} is omitted, it defaults to \code{'r'}. When opening a
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binary file, you should append \code{'b'} to the \var{mode} value
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for improved portability. (It's useful even on systems which don't
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treat binary and text files differently, where it serves as
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documentation.)
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\index{line-buffered I/O}\index{unbuffered I/O}\index{buffer size, I/O}
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\index{I/O control!buffering}
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The optional \var{bufsize} argument specifies the
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file's desired buffer size: 0 means unbuffered, 1 means line
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buffered, any other positive value means use a buffer of
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(approximately) that size. A negative \var{bufsize} means to use
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the system default, which is usually line buffered for for tty
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devices and fully buffered for other files. If omitted, the system
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default is used.\footnote{
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Specifying a buffer size currently has no effect on systems that
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don't have \cfunction{setvbuf()}. The interface to specify the
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buffer size is not done using a method that calls
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\cfunction{setvbuf()}, because that may dump core when called
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after any I/O has been performed, and there's no reliable way to
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determine whether this is the case.}
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The \function{file()} constructor is new in Python 2.2. The previous
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spelling, \function{open()}, is retained for compatibility, and is an
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alias for \function{file()}.
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\end{funcdesc}
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\begin{funcdesc}{filter}{function, list}
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Construct a list from those elements of \var{list} for which
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\var{function} returns true. \var{list} may be either a sequence, a
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container which supports iteration, or an iterator, If \var{list}
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is a string or a tuple, the result also has that type; otherwise it
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is always a list. If \var{function} is \code{None}, the identity
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function is assumed, that is, all elements of \var{list} that are false
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(zero or empty) are removed.
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\end{funcdesc}
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\begin{funcdesc}{float}{x}
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Convert a string or a number to floating point. If the argument is a
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string, it must contain a possibly signed decimal or floating point
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number, possibly embedded in whitespace; this behaves identical to
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\code{string.atof(\var{x})}. Otherwise, the argument may be a plain
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or long integer or a floating point number, and a floating point
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number with the same value (within Python's floating point
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precision) is returned.
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\strong{Note:} When passing in a string, values for NaN\index{NaN}
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and Infinity\index{Infinity} may be returned, depending on the
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underlying C library. The specific set of strings accepted which
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cause these values to be returned depends entirely on the C library
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and is known to vary.
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\end{funcdesc}
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\begin{funcdesc}{getattr}{object, name\optional{, default}}
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Return the value of the named attributed of \var{object}. \var{name}
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must be a string. If the string is the name of one of the object's
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attributes, the result is the value of that attribute. For example,
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\code{getattr(x, 'foobar')} is equivalent to \code{x.foobar}. If the
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named attribute does not exist, \var{default} is returned if provided,
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otherwise \exception{AttributeError} is raised.
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\end{funcdesc}
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\begin{funcdesc}{globals}{}
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Return a dictionary representing the current global symbol table.
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This is always the dictionary of the current module (inside a
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function or method, this is the module where it is defined, not the
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module from which it is called).
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\end{funcdesc}
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\begin{funcdesc}{hasattr}{object, name}
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The arguments are an object and a string. The result is 1 if the
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string is the name of one of the object's attributes, 0 if not.
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(This is implemented by calling \code{getattr(\var{object},
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\var{name})} and seeing whether it raises an exception or not.)
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\end{funcdesc}
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\begin{funcdesc}{hash}{object}
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Return the hash value of the object (if it has one). Hash values
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are integers. They are used to quickly compare dictionary
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keys during a dictionary lookup. Numeric values that compare equal
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have the same hash value (even if they are of different types, as is
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the case for 1 and 1.0).
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\end{funcdesc}
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\begin{funcdesc}{hex}{x}
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Convert an integer number (of any size) to a hexadecimal string.
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The result is a valid Python expression. Note: this always yields
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an unsigned literal. For example, on a 32-bit machine,
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\code{hex(-1)} yields \code{'0xffffffff'}. When evaluated on a
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machine with the same word size, this literal is evaluated as -1; at
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a different word size, it may turn up as a large positive number or
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raise an \exception{OverflowError} exception.
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\end{funcdesc}
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\begin{funcdesc}{id}{object}
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Return the `identity' of an object. This is an integer (or long
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integer) which is guaranteed to be unique and constant for this
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object during its lifetime. Two objects whose lifetimes are
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disjunct may have the same \function{id()} value. (Implementation
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note: this is the address of the object.)
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\end{funcdesc}
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\begin{funcdesc}{input}{\optional{prompt}}
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Equivalent to \code{eval(raw_input(\var{prompt}))}.
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\strong{Warning:} This function is not safe from user errors! It
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expects a valid Python expression as input; if the input is not
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syntactically valid, a \exception{SyntaxError} will be raised.
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Other exceptions may be raised if there is an error during
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evaluation. (On the other hand, sometimes this is exactly what you
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need when writing a quick script for expert use.)
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If the \module{readline} module was loaded, then
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\function{input()} will use it to provide elaborate line editing and
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history features.
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Consider using the \function{raw_input()} function for general input
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from users.
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\end{funcdesc}
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\begin{funcdesc}{int}{x\optional{, radix}}
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Convert a string or number to a plain integer. If the argument is a
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string, it must contain a possibly signed decimal number
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representable as a Python integer, possibly embedded in whitespace;
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this behaves identical to \code{string.atoi(\var{x}\optional{,
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\var{radix}})}. The \var{radix} parameter gives the base for the
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conversion and may be any integer in the range [2, 36], or zero. If
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\var{radix} is zero, the proper radix is guessed based on the
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contents of string; the interpretation is the same as for integer
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|
literals. 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 truncates (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 (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}{iter}{o\optional{, sentinel}}
|
|
Return an iterator object. The first argument is interpreted very
|
|
differently depending on the presence of the second argument.
|
|
Without a second argument, \var{o} must be a collection object which
|
|
supports the iteration protocol (the \method{__iter__()} method), or
|
|
it must support the sequence protocol (the \method{__getitem__()}
|
|
method with integer arguments starting at \code{0}). If it does not
|
|
support either of those protocols, \exception{TypeError} is raised.
|
|
If the second argument, \var{sentinel}, is given, then \var{o} must
|
|
be a callable object. The iterator created in this case will call
|
|
\var{o} with no arguments for each call to its \method{next()}
|
|
method; if the value returned is equal to \var{sentinel},
|
|
\exception{StopIteration} will be raised, otherwise the value will
|
|
be returned.
|
|
\versionadded{2.2}
|
|
\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. \var{sequence} may be either a sequence, a
|
|
container that supports iteration, or an iterator object. If
|
|
\var{sequence} is already a list, a copy is made and returned,
|
|
similar to \code{\var{sequence}[:]}. For instance,
|
|
\code{list('abc')} 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\optional{, radix}}
|
|
Convert a string or number to a long integer. If the argument is a
|
|
string, it must contain a possibly signed number of
|
|
arbitrary size, possibly embedded in whitespace;
|
|
this behaves identical to \code{string.atol(\var{x})}. The
|
|
\var{radix} argument is interpreted in the same way as for
|
|
\function{int()}, and may only be given when \var{x} is a string.
|
|
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 truncates (towards zero).
|
|
\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 (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 (such as 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 (such as 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. For example, 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}}}
|
|
An alias for the \function{file()} function above.
|
|
\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
|
|
coercion rules for binary arithmetic operators apply. For int and
|
|
long int operands, the result has the same type as the operands
|
|
(after coercion) unless the second argument is negative; in that
|
|
case, all arguments are converted to float and a float result is
|
|
delivered. For example, \code{10**2} returns \code{100}, but
|
|
\code{10**-2} returns \code{0.01}. (This last feature was added in
|
|
Python 2.2. In Python 2.1 and before, if both arguments were of integer
|
|
types and the second argument was negative, an exception was raised.)
|
|
If the second argument is negative, the third argument must be omitted.
|
|
If \var{z} is present, \var{x} and \var{y} must be of integer types,
|
|
and \var{y} must be non-negative. (This restriction was added in
|
|
Python 2.2. In Python 2.1 and before, floating 3-argument \code{pow()}
|
|
returned platform-dependent results depending on floating-point
|
|
rounding accidents.)
|
|
\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 (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 many 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. for example,
|
|
\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. For example: \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}. For example, \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\optional{, errors}}}
|
|
Create a Unicode string from an 8-bit string \var{string} using the
|
|
codec for \var{encoding}. The \var{encoding} parameter is a string
|
|
giving the name of an encoding. Error handling is done according to
|
|
\var{errors}; this specifies the treatment of characters which are
|
|
invalid in the input encoding. If \var{errors} is \code{'strict'}
|
|
(the default), a \exception{ValueError} is raised on errors, while a
|
|
value of \code{'ignore'} causes errors to be silently ignored, and a
|
|
value of \code{'replace'} causes the official Unicode replacement
|
|
character, \code{U+FFFD}, to be used to replace input characters which
|
|
cannot be decoded. The default behavior is to decode UTF-8 in strict
|
|
mode, meaning that encoding errors raise \exception{ValueError}. See
|
|
also the \refmodule{codecs} module.
|
|
\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 (such as 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 or when all of the range's elements are never used (such as
|
|
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 there are multiple argument sequences which
|
|
are all of the same length, \function{zip()} is similar to
|
|
\function{map()} with an initial argument of \code{None}. With a
|
|
single sequence argument, it returns a list of 1-tuples.
|
|
\versionadded{2.0}
|
|
\end{funcdesc}
|