\section{Built-in Functions}

\label{built-in-funcs}

The Python interpreter has a number of functions built into it that

are always available. They are listed here in alphabetical order.

\setindexsubitem{(built-in function)}

\begin{funcdesc}{__import__}{name\optional{, globals\optional{, locals\optional{, fromlist}}}}

This function is invoked by the \code{import} statement. It

mainly exists so that you can replace it with another

function that has a compatible interface, in order to change the

semantics of the \code{import} statement. For examples of why and

how you would do this, see the standard library modules \code{ni},

\code{ihooks} and \code{rexec}. See also the built-in module

\code{imp}, which defines some useful operations out of which you can

build your own \code{__import__()} function.

\stindex{import}

\refstmodindex{ni}

\refstmodindex{ihooks}

\refstmodindex{rexec}

\refbimodindex{imp}

For example, the statement \code{import spam} results in the following

call:

\code{__import__('spam', globals(), locals(), [])};

the statement \code{from spam.ham import eggs} results in

\code{__import__('spam.ham', globals(), locals(), ['eggs'])}.

Note that even though \code{locals()} and \code{['eggs']} are passed

in as arguments, the \code{__import__()} function does not set the

local variable named \code{eggs}; this is done by subsequent code that

is generated for the import statement. (In fact, the standard

implementation does not use its \var{locals} argument at all, and uses

its \var{globals} only to determine the package context of the

\code{import} statement.)

When the \var{name} variable is of the form \code{package.module},

normally, the top-level package (the name up till the first dot) is

returned, \emph{not} the module named by \var{name}. However, when a

non-empty \var{fromlist} argument is given, the module named by

\var{name} is returned. This is done for compatibility with the

bytecode generated for the different kinds of import statement; when

using \code{import spam.ham.eggs}, the top-level package \code{spam}

must be placed in the importing namespace, but when using \code{from

spam.ham import eggs}, the \code{spam.ham} subpackage must be used to

find the \code{eggs} variable.

\end{funcdesc}

\begin{funcdesc}{abs}{x}

Return the absolute value of a number. The argument may be a plain

or long integer or a floating point number. If the argument is a

complex number, its magnitude is returned.

\end{funcdesc}

\begin{funcdesc}{apply}{function\, args\optional{, keywords}}

The \var{function} argument must be a callable object (a user-defined or

built-in function or method, or a class object) and the \var{args}

argument must be a 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.)

If the optional \var{keywords} argument is present, it must be a

dictionary whose keys are strings. It specifies keyword arguments to

be added to the end of the the argument list.

\end{funcdesc}

\begin{funcdesc}{callable}{object}

Return true if the \var{object} argument appears callable, false if

not. If this returns true, it is still possible that a call fails,

but if it is false, calling \var{object} will never succeed. Note

that classes are callable (calling a class returns a new instance);

class instances are callable if they have an attribute \code{__call__}.

\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 an \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, \code{'eval'}

if it consists of a single expression, or \code{'single'} if

it consists of a single interactive statement (in the latter case,

expression statements that evaluate to something else than

\code{None} will printed).

\end{funcdesc}

\begin{funcdesc}{complex}{real\optional{, imag}}

Create a complex number with the value \var{real} + \var{imag}*j.

Each argument may be any numeric type (including complex).

If \var{imag} is omitted, it defaults to zero and the function

serves as a numeric conversion function like \code{int}, \code{long}

and \code{float}.

\end{funcdesc}

\begin{funcdesc}{delattr}{object\, name}

This is a relative of \code{setattr}. The arguments are an

object and a string. The string must be the name

of one of the object's attributes. The function deletes

the named attribute, provided the object allows it. For example,

\code{delattr(\var{x}, '\var{foobar}')} is equivalent to

\code{del \var{x}.\var{foobar}}.

\end{funcdesc}

\begin{funcdesc}{dir}{}

Without arguments, return the list of names in the current local

symbol table. With an argument, attempts to return a list of valid

attribute for that object. This information is gleaned from the

object's \code{__dict__}, \code{__methods__} and \code{__members__}

attributes, if defined. The list is not necessarily complete; e.g.,

for classes, attributes defined in base classes are not included,

and for class instances, methods are not included.

The resulting list is sorted alphabetically. For example:

\begin{verbatim}

>>> import sys

>>> dir()

['sys']

>>> dir(sys)

['argv', 'exit', 'modules', 'path', 'stderr', 'stdin', 'stdout']

>>>

\end{verbatim}

\end{funcdesc}

\begin{funcdesc}{divmod}{a\, b}

Take two numbers as arguments and return a pair of numbers consisting

of their quotient and remainder when using long division. With mixed

operand types, the rules for binary arithmetic operators apply. For

plain and long integers, the result is the same as

\code{(\var{a} / \var{b}, \var{a} \%{} \var{b})}.

For floating point numbers the result is the same as

\code{(math.floor(\var{a} / \var{b}), \var{a} \%{} \var{b})}.

\end{funcdesc}

\begin{funcdesc}{eval}{expression\optional{\, globals\optional{\, locals}}}

The arguments are a string and two optional dictionaries. The

\var{expression} argument is parsed and evaluated as a Python

expression (technically speaking, a condition list) using the

\var{globals} and \var{locals} dictionaries as global and local name

space. If the \var{locals} dictionary is omitted it defaults to

the \var{globals} dictionary. If both dictionaries are omitted, the

expression is executed in the environment where \code{eval} is

called. The return value is the result of the evaluated expression.

Syntax errors are reported as exceptions. Example:

\begin{verbatim}

>>> x = 1

>>> print eval('x+1')

2

>>>

\end{verbatim}

%

This function can also be used to execute arbitrary code objects

(e.g.\ created by \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.

Hints: dynamic execution of statements is supported by the

\code{exec} statement. Execution of statements from a file is

supported by the \code{execfile()} function. The \code{globals()}

and \code{locals()} functions returns the current global and local

dictionary, respectively, which may be useful

to pass around for use by \code{eval()} or \code{execfile()}.

\end{funcdesc}

\begin{funcdesc}{execfile}{file\optional{\, globals\optional{\, locals}}}

This function is similar to the

\code{exec} statement, but parses a file instead of a string. It is

different from the \code{import} statement in that it does not use

the module administration --- it reads the file unconditionally and

does not create a new module.\footnote{It is used relatively rarely

so does not warrant being made into a statement.}

The arguments are a file name and two optional dictionaries. The

file is parsed and evaluated as a sequence of Python statements

(similarly to a module) using the \var{globals} and \var{locals}

dictionaries as global and local name space. If the \var{locals}

dictionary is omitted it defaults to the \var{globals} dictionary.

If both dictionaries are omitted, the expression is executed in the

environment where \code{execfile()} is called. The return value is

\code{None}.

\end{funcdesc}

\begin{funcdesc}{filter}{function\, list}

Construct a list from those elements of \var{list} for which

\var{function} returns true. If \var{list} is a string or a tuple,

the result also has that type; otherwise it is always a list. If

\var{function} is \code{None}, the identity function is assumed,

i.e.\ all elements of \var{list} that are false (zero or empty) are

removed.

\end{funcdesc}

\begin{funcdesc}{float}{x}

Convert a string or a number to floating point. If the argument is a

string, it must contain a possibly singed decimal or floating point

number, possibly embedded in whitespace;

this behaves identical to \code{string.atof(\var{x})}.

Otherwise, the argument may be a plain or

long integer or a floating point number, and a floating point number

with the same value (within Python's floating point precision) is

returned.

\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}{globals}{}

Return a dictionary representing the current global symbol table.

This is always the dictionary of the current module (inside a

function or method, this is the module where it is defined, not the

module from which it is called).

\end{funcdesc}

\begin{funcdesc}{hasattr}{object\, name}

The arguments are an object and a string. The result is 1 if the

string is the name of one of the object's attributes, 0 if not.

(This is implemented by calling \code{getattr(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 integers. They are used to quickly compare dictionary

keys during a dictionary lookup. Numeric values that compare equal

have the same hash value (even if they are of different types, e.g.

1 and 1.0).

\end{funcdesc}

\begin{funcdesc}{hex}{x}

Convert an integer number (of any size) to a hexadecimal string.

The result is a valid Python expression. Note: this always yields

an unsigned literal, e.g. on a 32-bit machine, \code{hex(-1)} yields

\code{'0xffffffff'}. When evaluated on a machine with the same

word size, this literal is evaluated as -1; at a different word

size, it may turn up as a large positive number or raise an

\code{OverflowError} exception.

\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, and the

\code{readline} module is used when loaded. The difference

is that a long input expression may be broken over multiple lines using

the backslash convention.

\end{funcdesc}

\begin{funcdesc}{intern}{string}

Enter \var{string} in the table of ``interned'' strings and return

the interned string -- which is \var{string} itself or a copy.

Interning strings is useful to gain a little performance on

dictionary lookup -- if the keys in a dictionary are interned, and

the lookup key is interned, the key comparisons (after hashing) can

be done by a pointer compare instead of a string compare. Normally,

the names used in Python programs are automatically interned, and

the dictionaries used to hold module, class or instance attributes

have interned keys. Interned strings are immortal (i.e. never get

garbage collected).

\end{funcdesc}

\begin{funcdesc}{int}{x}

Convert a string or number to a plain integer. If the argument is a

string, it must contain a possibly singed decimal number

representable as a Python integer, possibly embedded in whitespace;

this behaves identical to \code{string.atoi(\var{x})}.

Otherwise, the argument may be a plain or

long integer or a floating point number. Conversion of floating

point numbers to integers is defined by the C semantics; normally

the conversion truncates towards zero.\footnote{This is ugly --- the

language definition should require truncation towards zero.}

\end{funcdesc}

\begin{funcdesc}{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

\code{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 \code{TypeError} exception is raised.

\end{funcdesc}

\begin{funcdesc}{len}{s}

Return the length (the number of items) of an object. The argument

may be a sequence (string, tuple or list) or a mapping (dictionary).

\end{funcdesc}

\begin{funcdesc}{list}{sequence}

Return a list whose items are the same and in the same order as

\var{sequence}'s items. If \var{sequence} is already a list,

a copy is made and returned, similar to \code{\var{sequence}[:]}.

For instance, \code{list('abc')} returns

returns \code{['a', 'b', 'c']} and \code{list( (1, 2, 3) )} returns

\code{[1, 2, 3]}.

\end{funcdesc}

\begin{funcdesc}{locals}{}

Return a dictionary representing the current local symbol table.

Inside a function, modifying this dictionary does not always have the

desired effect.

\end{funcdesc}

\begin{funcdesc}{long}{x}

Convert a string or number to a long integer. If the argument is a

string, it must contain a possibly singed decimal number of

arbitrary size, possibly embedded in whitespace;

this behaves identical to \code{string.atol(\var{x})}.

Otherwise, the argument may be a plain or

long integer or a floating point number, and a long integer with

the same value is returned. Conversion of floating

point numbers to integers is defined by the C semantics;

see the description of \code{int()}.

\end{funcdesc}

\begin{funcdesc}{map}{function\, list\, ...}

Apply \var{function} to every item of \var{list} and return a list

of the results. If additional \var{list} arguments are passed,

\var{function} must take that many arguments and is applied to

the items of all lists in parallel; if a list is shorter than another

it is assumed to be extended with \code{None} items. If

\var{function} is \code{None}, the identity function is assumed; if

there are multiple list arguments, \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 an integer number (of any size) to an octal string. The

result is a valid Python expression. Note: this always yields

an unsigned literal, e.g. on a 32-bit machine, \code{oct(-1)} yields

\code{'037777777777'}. When evaluated on a machine with the same

word size, this literal is evaluated as -1; at a different word

size, it may turn up as a large positive number or raise an

\code{OverflowError} exception.

\end{funcdesc}

\begin{funcdesc}{open}{filename\optional{\, mode\optional{\, bufsize}}}

Return a new file object (described earlier under Built-in Types).

The first two arguments are the same as for \code{stdio}'s

\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 (which on \emph{some} \UNIX{}

systems means that \emph{all} writes append to the end of the file,

regardless of the current seek position).

Modes \code{'r+'}, \code{'w+'} and

\code{'a+'} open the file for updating, 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, return

\var{x} to the power \var{y}, modulo \var{z} (computed more

efficiently than \code{pow(\var{x}, \var{y}) \% \var{z}}).

The arguments must have

numeric types. With mixed operand types, the rules for binary

arithmetic operators apply. The effective operand type is also the

type of the result; if the result is not expressible in this type, the

function raises an exception; e.g., \code{pow(2, -1)} or \code{pow(2,

35000)} is not allowed.

\end{funcdesc}

\begin{funcdesc}{range}{\optional{start\,} stop\optional{\, step}}

This is a versatile function to create lists containing arithmetic

progressions. It is most often used in \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{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 an

exception 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, \code{EOFError} is raised. Example:

\begin{verbatim}

>>> s = raw_input('--> ')

--> Monty Python's Flying Circus

>>> s

"Monty Python's Flying Circus"

>>>

\end{verbatim}

If the \code{readline} module was loaded, then

\code{raw_input()} will use it to provide elaborate

line editing and history features.

\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. The return value is the

module object (i.e.\ the same as the \var{module} argument).

There are a number of caveats:

If a module is syntactically correct but its initialization fails, the

first \code{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

\code{import} it again (this will bind the name to the partially

initialized module object) before you can \code{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 \code{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 \code{sys}, \code{__main__} and

\code{__builtin__}. In certain cases, however, extension modules are

not designed to be initialized more than once, and may fail in

arbitrary ways when reloaded.

If a module imports objects from another module using \code{from}

\ldots{} \code{import} \ldots{}, calling \code{reload()} for the other

module does not redefine the objects imported from it --- one way

around this is to re-execute the \code{from} statement, another is to

use \code{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 \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}{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 \code{start}, \code{stop} and \code{step}

which merely return the argument values (or their default). They have

no other explicit functionality; however they are used by Numerical

Python and other third party extensions. Slice objects are also

generated when extended indexing syntax is used, e.g. for

\code{a[start:stop:step]} or \code{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 \code{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 \code{types} defines names for all

built-in types.

\refstmodindex{types}

\obindex{type}

For instance:

\begin{verbatim}

>>> import types

>>> if isinstance(x, types.StringType): print "It's a string"

\end{verbatim}

\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 \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 (e.g. modules) can be. This may change.}

\end{funcdesc}

\begin{funcdesc}{xrange}{\optional{start\,} stop\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. MS-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}