The Python interpreter has a number of functions built into it that are always available. They are listed here in alphabetical order.
In addition, there are other four built-in functions that are no longer
considered essential: apply()
, buffer()
, coerce()
, and
intern()
. They are documented in the Non-essential Built-in Functions
section.
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.
all(iterable)
Return True
if all elements of the iterable are true (or if the iterable
is empty). Equivalent to:
def all(iterable):
for element in iterable:
if not element:
return False
return True
New in version 2.5.
any(iterable)
Return True
if any element of the iterable is true. If the iterable
is empty, return False
. Equivalent to:
def any(iterable):
for element in iterable:
if element:
return True
return False
New in version 2.5.
basestring()
This abstract type is the superclass for str
and unicode
. It
cannot be called or instantiated, but it can be used to test whether an object
is an instance of str
or unicode
. isinstance(obj,
basestring)
is equivalent to isinstance(obj, (str, unicode))
.
New in version 2.3.
bin(x)
Convert an integer number to a binary string. The result is a valid Python
expression. If x is not a Python int
object, it has to define an
__index__()
method that returns an integer.
New in version 2.6.
class bool([x])
Return a Boolean value, i.e. one of True
or False
. x is converted
using the standard truth testing procedure. If x is false or omitted, this
returns False
; otherwise it returns True
. bool
is
also a class, which is a subclass of int
. Class bool
cannot
be subclassed further. Its only instances are False
and
True
.
New in version 2.2.1.
Changed in version 2.3: If no argument is given, this function returns False
.
class bytearray([source[, encoding[, errors]]])
Return a new array of bytes. The bytearray
class is a mutable
sequence of integers in the range 0 <= x < 256. It has most of the usual
methods of mutable sequences, described in Mutable Sequence Types, as well
as most methods that the str
type has, see String Methods.
The optional source parameter can be used to initialize the array in a few different ways:
- If it is unicode, you must also give the encoding (and optionally,
errors) parameters;
bytearray()
then converts the unicode to bytes usingunicode.encode()
. - If it is an integer, the array will have that size and will be initialized with null bytes.
- If it is an object conforming to the buffer interface, a read-only buffer of the object will be used to initialize the bytes array.
- If it is an iterable, it must be an iterable of integers in the range
0 <= x < 256
, which are used as the initial contents of the array.
Without an argument, an array of size 0 is created.
New in version 2.6.
callable(object)
Return True
if the 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 object will never succeed. Note that classes are callable (calling a
class returns a new instance); class instances are callable if they have a
__call__()
method.
chr(i)
Return a string of one character whose ASCII code is the integer i. For
example, chr(97)
returns the string 'a'
. This is the inverse of
ord()
. The argument must be in the range [0..255], inclusive;
ValueError
will be raised if i is outside that range. See
also unichr()
.
classmethod(function)
Return a class method for function.
A class method receives the class as implicit first argument, just like an instance method receives the instance. To declare a class method, use this idiom:
class C(object):
@classmethod
def f(cls, arg1, arg2, ...):
...
The @classmethod
form is a function decorator -- see the description
of function definitions in Function definitions for details.
It can be called either on the class (such as C.f()
) or on an instance (such
as C().f()
). The instance is ignored except for its class. If a class
method is called for a derived class, the derived class object is passed as the
implied first argument.
Class methods are different than C++ or Java static methods. If you want those,
see staticmethod()
in this section.
For more information on class methods, consult the documentation on the standard type hierarchy in The standard type hierarchy.
New in version 2.2.
Changed in version 2.4: Function decorator syntax added.
cmp(x, y)
Compare the two objects x and y and return an integer according to the
outcome. The return value is negative if x < y
, zero if x == y
and
strictly positive if x > y
.
compile(source, filename, mode[, flags[, dont_inherit]])
Compile the source into a code or AST object. Code objects can be executed
by an exec
statement or evaluated by a call to eval()
.
source can either be a Unicode string, a Latin-1 encoded string or an
AST object.
Refer to the ast
module documentation for information on how to work
with AST objects.
The filename argument should give the file from which the code was read;
pass some recognizable value if it wasn't read from a file ('<string>'
is
commonly used).
The mode argument specifies what kind of code must be compiled; it can be
'exec'
if source consists of a sequence of statements, 'eval'
if it
consists of a single expression, or 'single'
if it consists of a single
interactive statement (in the latter case, expression statements that
evaluate to something other than None
will be printed).
The optional arguments flags and dont_inherit control which future
statements (see PEP 236) affect the compilation of source. If neither
is present (or both are zero) the code is compiled with those future
statements that are in effect in the code that is calling compile()
. If the
flags argument is given and dont_inherit is not (or is zero) then the
future statements specified by the flags argument are used in addition to
those that would be used anyway. If dont_inherit is a non-zero integer then
the flags argument is it -- the future statements in effect around the call
to compile are ignored.
Future statements are specified by bits which can be bitwise ORed together to
specify multiple statements. The bitfield required to specify a given feature
can be found as the compiler_flag
attribute on
the _Feature
instance in the __future__
module.
This function raises SyntaxError
if the compiled source is invalid,
and TypeError
if the source contains null bytes.
If you want to parse Python code into its AST representation, see
ast.parse()
.
Note
When compiling a string with multi-line code in 'single'
or
'eval'
mode, input must be terminated by at least one newline
character. This is to facilitate detection of incomplete and complete
statements in the code
module.
Changed in version 2.3: The flags and dont_inherit arguments were added.
Changed in version 2.6: Support for compiling AST objects.
Changed in version 2.7: Allowed use of Windows and Mac newlines. Also input in 'exec'
mode
does not have to end in a newline anymore.
class complex([real[, imag]])
Return a complex number with the value real + imag*1j or convert a string or
number to a complex number. If the first parameter is a string, it will be
interpreted as a complex number and the function must be called without a second
parameter. The second parameter can never be a string. Each argument may be any
numeric type (including complex). If imag is omitted, it defaults to zero and
the function serves as a numeric conversion function like int()
,
long()
and float()
. If both arguments are omitted, returns 0j
.
Note
When converting from a string, the string must not contain whitespace
around the central +
or -
operator. For example,
complex('1+2j')
is fine, but complex('1 + 2j')
raises
ValueError
.
The complex type is described in Numeric Types --- int, float, long, complex.
delattr(object, name)
This is a relative of 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, delattr(x, 'foobar')
is equivalent to del x.foobar
.
class dict(**kwarg)
class dict(mapping, **kwarg)
class dict(iterable, **kwarg)
Create a new dictionary. The dict
object is the dictionary class.
See dict
and Mapping Types --- dict for documentation about this class.
For other containers see the built-in list
, set
, and
tuple
classes, as well as the collections
module.
dir([object])
Without arguments, return the list of names in the current local scope. With an argument, attempt to return a list of valid attributes for that object.
If the object has a method named __dir__()
, this method will be called and
must return the list of attributes. This allows objects that implement a custom
__getattr__()
or __getattribute__()
function to customize the way
dir()
reports their attributes.
If the object does not provide __dir__()
, the function tries its best to
gather information from the object's __dict__
attribute, if defined, and
from its type object. The resulting list is not necessarily complete, and may
be inaccurate when the object has a custom __getattr__()
.
The default dir()
mechanism behaves differently with different types of
objects, as it attempts to produce the most relevant, rather than complete,
information:
- If the object is a module object, the list contains the names of the module's attributes.
- If the object is a type or class object, the list contains the names of its attributes, and recursively of the attributes of its bases.
- Otherwise, the list contains the object's attributes' names, the names of its class's attributes, and recursively of the attributes of its class's base classes.
The resulting list is sorted alphabetically. For example:
[UNKNOWN NODE doctest_block]Note
Because dir()
is supplied primarily as a convenience for use at an
interactive prompt, it tries to supply an interesting set of names more than it
tries to supply a rigorously or consistently defined set of names, and its
detailed behavior may change across releases. For example, metaclass attributes
are not in the result list when the argument is a class.
divmod(a, b)
Take two (non complex) 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 (a // b, a % b)
. For floating point
numbers the result is (q, a % b)
, where q is usually math.floor(a / b)
but may be 1 less than that. In any case q * b + a % b
is very close to
a, if a % b
is non-zero it has the same sign as b, and 0 <= abs(a % b)
< abs(b)
.
Changed in version 2.3: Using divmod()
with complex numbers is deprecated.
enumerate(sequence, start=0)
Return an enumerate object. sequence must be a sequence, an
iterator, or some other object which supports iteration. The
next()
method of the iterator returned by enumerate()
returns a
tuple containing a count (from start which defaults to 0) and the
values obtained from iterating over sequence:
>>> seasons = ['Spring', 'Summer', 'Fall', 'Winter']
>>> list(enumerate(seasons))
[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]
>>> list(enumerate(seasons, start=1))
[(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]
Equivalent to:
def enumerate(sequence, start=0):
n = start
for elem in sequence:
yield n, elem
n += 1
New in version 2.3.
Changed in version 2.6: The start parameter was added.
eval(expression[, globals[, locals]])
The arguments are a Unicode or Latin-1 encoded string and optional globals and locals. If provided, globals must be a dictionary. If provided, locals can be any mapping object.
Changed in version 2.4: formerly locals was required to be a dictionary.
The expression argument is parsed and evaluated as a Python expression
(technically speaking, a condition list) using the globals and locals
dictionaries as global and local namespace. If the globals dictionary is
present and lacks '__builtins__', the current globals are copied into globals
before expression is parsed. This means that expression normally has full
access to the standard __builtin__
module and restricted environments are
propagated. If the locals dictionary is omitted it defaults to the globals
dictionary. If both dictionaries are omitted, the expression is executed in the
environment where eval()
is called. The return value is the result of
the evaluated expression. Syntax errors are reported as exceptions. Example:
This function can also be used to execute arbitrary code objects (such as
those created by compile()
). In this case pass a code object instead
of a string. If the code object has been compiled with 'exec'
as the
mode argument, eval()
's return value will be None
.
Hints: dynamic execution of statements is supported by the exec
statement. Execution of statements from a file is supported by the
execfile()
function. The globals()
and locals()
functions
returns the current global and local dictionary, respectively, which may be
useful to pass around for use by eval()
or execfile()
.
See ast.literal_eval()
for a function that can safely evaluate strings
with expressions containing only literals.
execfile(filename[, globals[, locals]])
This function is similar to the exec
statement, but parses a file
instead of a string. It is different from the import
statement in
that it does not use the module administration --- it reads the file
unconditionally and does not create a new module. 1
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 globals and locals dictionaries as global and local namespace. If provided, locals can be any mapping object. Remember that at module level, globals and locals are the same dictionary. If two separate objects are passed as globals and locals, the code will be executed as if it were embedded in a class definition.
Changed in version 2.4: formerly locals was required to be a dictionary.
If the locals dictionary is omitted it defaults to the globals dictionary.
If both dictionaries are omitted, the expression is executed in the environment
where execfile()
is called. The return value is None
.
Note
The default locals act as described for function locals()
below:
modifications to the default locals dictionary should not be attempted. Pass
an explicit locals dictionary if you need to see effects of the code on
locals after function execfile()
returns. execfile()
cannot be
used reliably to modify a function's locals.
file(name[, mode[, buffering]])
Constructor function for the file
type, described further in section
File Objects. The constructor's arguments are the same as those
of the open()
built-in function described below.
When opening a file, it's preferable to use open()
instead of invoking
this constructor directly. file
is more suited to type testing (for
example, writing isinstance(f, file)
).
New in version 2.2.
filter(function, iterable)
Construct a list from those elements of iterable for which function returns
true. iterable may be either a sequence, a container which supports
iteration, or an iterator. If iterable is a string or a tuple, the result
also has that type; otherwise it is always a list. If function is None
,
the identity function is assumed, that is, all elements of iterable that are
false are removed.
Note that filter(function, iterable)
is equivalent to [item for item in
iterable if function(item)]
if function is not None
and [item for item
in iterable if item]
if function is None
.
See itertools.ifilter()
and itertools.ifilterfalse()
for iterator
versions of this function, including a variation that filters for elements
where the function returns false.
class float([x])
Return a floating point number constructed from a number or string x.
If the argument is a string, it
must contain a possibly signed decimal or floating point number, possibly
embedded in whitespace. The argument may also be [+|-]nan or [+|-]inf.
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. If no argument is
given, returns 0.0
.
Note
When passing in a string, values for NaN and Infinity may be returned, depending on the underlying C library. Float accepts the strings nan, inf and -inf for NaN and positive or negative infinity. The case and a leading + are ignored as well as a leading - is ignored for NaN. Float always represents NaN and infinity as nan, inf or -inf.
The float type is described in Numeric Types --- int, float, long, complex.
format(value[, format_spec])
Convert a value to a "formatted" representation, as controlled by format_spec. The interpretation of format_spec will depend on the type of the value argument, however there is a standard formatting syntax that is used by most built-in types: Format Specification Mini-Language.
Note
format(value, format_spec)
merely calls
value.__format__(format_spec)
.
New in version 2.6.
class frozenset([iterable])
Return a new frozenset
object, optionally with elements taken from
iterable. frozenset
is a built-in class. See frozenset
and
Set Types --- set, frozenset for documentation about this class.
For other containers see the built-in set
, list
,
tuple
, and dict
classes, as well as the collections
module.
New in version 2.4.
getattr(object, name[, default])
Return the value of the named attribute of object. name must be a string.
If the string is the name of one of the object's attributes, the result is the
value of that attribute. For example, getattr(x, 'foobar')
is equivalent to
x.foobar
. If the named attribute does not exist, default is returned if
provided, otherwise AttributeError
is raised.
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).
hasattr(object, name)
The arguments are an object and a string. The result is True
if the string
is the name of one of the object's attributes, False
if not. (This is
implemented by calling getattr(object, name)
and seeing whether it raises an
exception or not.)
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, as is the case for 1 and 1.0).
help([object])
Invoke the built-in help system. (This function is intended for interactive use.) If no argument is given, the interactive help system starts on the interpreter console. If the argument is a string, then the string is looked up as the name of a module, function, class, method, keyword, or documentation topic, and a help page is printed on the console. If the argument is any other kind of object, a help page on the object is generated.
This function is added to the built-in namespace by the site
module.
New in version 2.2.
hex(x)
Convert an integer number (of any size) to a lowercase hexadecimal string prefixed with "0x", for example:
[UNKNOWN NODE doctest_block]If x is not a Python int
or long
object, it has to
define a __hex__() method that returns a string.
See also int()
for converting a hexadecimal string to an
integer using a base of 16.
Note
To obtain a hexadecimal string representation for a float, use the
float.hex()
method.
Changed in version 2.4: Formerly only returned an unsigned literal.
id(object)
Return the "identity" of an object. This is an integer (or long integer) which
is guaranteed to be unique and constant for this object during its lifetime.
Two objects with non-overlapping lifetimes may have the same id()
value.
CPython implementation detail: This is the address of the object in memory.
input([prompt])
Equivalent to eval(raw_input(prompt))
.
This function does not catch user errors. If the input is not syntactically
valid, a SyntaxError
will be raised. Other exceptions may be raised if
there is an error during evaluation.
If the readline
module was loaded, then input()
will use it to
provide elaborate line editing and history features.
Consider using the raw_input()
function for general input from users.
class int(x=0)
class int(x, base=10)
Return an integer object constructed from a number or string x, or return 0
if no
arguments are given. If x is a number, it can be a plain integer, a long
integer, or a floating point number. If x is floating point, the conversion
truncates towards zero. If the argument is outside the integer range, the
function returns a long object instead.
If x is not a number or if base is given, then x must be a string or
Unicode object representing an integer literal in radix
base. Optionally, the literal can be
preceded by +
or -
(with no space in between) and surrounded by
whitespace. A base-n literal consists of the digits 0 to n-1, with a
to z
(or A
to Z
) having
values 10 to 35. The default base is 10. The allowed values are 0 and 2--36.
Base-2, -8, and -16 literals can be optionally prefixed with 0b
/0B
,
0o
/0O
/0
, or 0x
/0X
, as with integer literals in code.
Base 0 means to interpret the string exactly as an integer literal, so that
the actual base is 2, 8, 10, or 16.
The integer type is described in Numeric Types --- int, float, long, complex.
isinstance(object, classinfo)
Return true if the object argument is an instance of the classinfo argument,
or of a (direct, indirect or virtual) subclass
thereof. Also return true if classinfo
is a type object (new-style class) and object is an object of that type or of
a (direct, indirect or virtual) subclass
thereof. If object is not a class instance or
an object of the given type, the function always returns false.
If classinfo is a tuple of class or type objects (or recursively, other
such tuples), return true if object is an instance of any of the classes
or types. If classinfo is not a class, type, or tuple of classes, types,
and such tuples, a TypeError
exception is raised.
Changed in version 2.2: Support for a tuple of type information was added.
issubclass(class, classinfo)
Return true if class is a subclass (direct, indirect or virtual) of classinfo. A
class is considered a subclass of itself. classinfo may be a tuple of class
objects, in which case every entry in classinfo will be checked. In any other
case, a TypeError
exception is raised.
Changed in version 2.3: Support for a tuple of type information was added.
iter(o[, sentinel])
Return an iterator object. The first argument is interpreted very differently
depending on the presence of the second argument. Without a second argument, o
must be a collection object which supports the iteration protocol (the
__iter__()
method), or it must support the sequence protocol (the
__getitem__()
method with integer arguments starting at 0
). If it
does not support either of those protocols, TypeError
is raised. If the
second argument, sentinel, is given, then o must be a callable object. The
iterator created in this case will call o with no arguments for each call to
its next()
method; if the value returned is equal to sentinel,
StopIteration
will be raised, otherwise the value will be returned.
One useful application of the second form of iter()
is to read lines of
a file until a certain line is reached. The following example reads a file
until the readline()
method returns an empty string:
with open('mydata.txt') as fp:
for line in iter(fp.readline, ''):
process_line(line)
New in version 2.2.
len(s)
Return the length (the number of items) of an object. The argument may be a sequence (such as a string, bytes, tuple, list, or range) or a collection (such as a dictionary, set, or frozen set).
class list([iterable])
Return a list whose items are the same and in the same order as iterable's
items. iterable may be either a sequence, a container that supports
iteration, or an iterator object. If iterable is already a list, a copy is
made and returned, similar to iterable[:]
. For instance, list('abc')
returns ['a', 'b', 'c']
and list( (1, 2, 3) )
returns [1, 2, 3]
. If
no argument is given, returns a new empty list, []
.
list
is a mutable sequence type, as documented in
Sequence Types --- str, unicode, list, tuple, bytearray, buffer, xrange. For other containers see the built in dict
,
set
, and tuple
classes, and the collections
module.
locals()
Update and return a dictionary representing the current local symbol table.
Free variables are returned by locals()
when it is called in function
blocks, but not in class blocks.
Note
The contents of this dictionary should not be modified; changes may not affect the values of local and free variables used by the interpreter.
class long(x=0)
class long(x, base=10)
Return a long integer object constructed from a string or number x.
If the argument is a string, it
must contain a possibly signed number of arbitrary size, possibly embedded in
whitespace. The base argument is interpreted in the same way as for
int()
, and may only be given when 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). If no arguments are given, returns 0L
.
The long type is described in Numeric Types --- int, float, long, complex.
map(function, iterable, ...)
Apply function to every item of iterable and return a list of the results.
If additional iterable arguments are passed, function must take that many
arguments and is applied to the items from all iterables in parallel. If one
iterable is shorter than another it is assumed to be extended with None
items. If function is None
, the identity function is assumed; if there
are multiple arguments, map()
returns a list consisting of tuples
containing the corresponding items from all iterables (a kind of transpose
operation). The iterable arguments may be a sequence or any iterable object;
the result is always a list.
max(iterable[, key])
max(arg1, arg2, *args[, key])
Return the largest item in an iterable or the largest of two or more arguments.
If one positional argument is provided, iterable must be a non-empty iterable (such as a non-empty string, tuple or list). The largest item in the iterable is returned. If two or more positional arguments are provided, the largest of the positional arguments is returned.
The optional key argument specifies a one-argument ordering function like that
used for list.sort()
. The key argument, if supplied, must be in keyword
form (for example, max(a,b,c,key=func)
).
Changed in version 2.5: Added support for the optional key argument.
memoryview(obj)
Return a "memory view" object created from the given argument. See memoryview type for more information.
min(iterable[, key])
min(arg1, arg2, *args[, key])
Return the smallest item in an iterable or the smallest of two or more arguments.
If one positional argument is provided, iterable must be a non-empty iterable (such as a non-empty string, tuple or list). The smallest item in the iterable is returned. If two or more positional arguments are provided, the smallest of the positional arguments is returned.
The optional key argument specifies a one-argument ordering function like that
used for list.sort()
. The key argument, if supplied, must be in keyword
form (for example, min(a,b,c,key=func)
).
Changed in version 2.5: Added support for the optional key argument.
next(iterator[, default])
Retrieve the next item from the iterator by calling its
next()
method. If default is given, it is returned if the
iterator is exhausted, otherwise StopIteration
is raised.
New in version 2.6.
class object
Return a new featureless object. object
is a base for all new style
classes. It has the methods that are common to all instances of new style
classes.
New in version 2.2.
Changed in version 2.3: This function does not accept any arguments. Formerly, it accepted arguments but ignored them.
oct(x)
Convert an integer number (of any size) to an octal string. The result is a valid Python expression.
Changed in version 2.4: Formerly only returned an unsigned literal.
open(name[, mode[, buffering]])
Open a file, returning an object of the file
type described in
section File Objects. If the file cannot be opened,
IOError
is raised. When opening a file, it's preferable to use
open()
instead of invoking the file
constructor directly.
The first two arguments are the same as for stdio
's fopen()
:
name is the file name to be opened, and mode is a string indicating how
the file is to be opened.
The most commonly-used values of mode are 'r'
for reading, 'w'
for
writing (truncating the file if it already exists), and 'a'
for appending
(which on some Unix systems means that all writes append to the end of the
file regardless of the current seek position). If mode is omitted, it
defaults to 'r'
. The default is to use text mode, which may convert
'\n'
characters to a platform-specific representation on writing and back
on reading. Thus, when opening a binary file, you should append 'b'
to
the mode value to open the file in binary mode, which will improve
portability. (Appending 'b'
is useful even on systems that don't treat
binary and text files differently, where it serves as documentation.) See below
for more possible values of mode.
The optional buffering 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 (in bytes). A negative buffering means to use the system default, which is usually line buffered for tty devices and fully buffered for other files. If omitted, the system default is used. 2
Modes 'r+'
, 'w+'
and 'a+'
open the file for updating (reading and writing);
note that 'w+'
truncates the file. Append 'b'
to the mode to open the file in
binary mode, on systems that differentiate between binary and text files; on
systems that don't have this distinction, adding the 'b'
has no effect.
In addition to the standard fopen()
values mode may be 'U'
or
'rU'
. Python is usually built with universal newlines support;
supplying 'U'
opens the file as a text file, but lines may be terminated
by any of the following: the Unix end-of-line convention '\n'
, the
Macintosh convention '\r'
, or the Windows convention '\r\n'
. All of
these external representations are seen as '\n'
by the Python program.
If Python is built without universal newlines support a mode with 'U'
is the same as normal text mode. Note that file objects so opened also have
an attribute called newlines
which has a value of None
(if no
newlines have yet been seen), '\n'
, '\r'
, '\r\n'
, or a tuple
containing all the newline types seen.
Python enforces that the mode, after stripping 'U'
, begins with 'r'
,
'w'
or 'a'
.
Python provides many file handling modules including
fileinput
, os
, os.path
, tempfile
, and
shutil
.
Changed in version 2.5: Restriction on first letter of mode string introduced.
ord(c)
Given a string of length one, return an integer representing the Unicode code
point of the character when the argument is a unicode object, or the value of
the byte when the argument is an 8-bit string. For example, ord('a')
returns
the integer 97
, ord(u'\u2020')
returns 8224
. This is the inverse of
chr()
for 8-bit strings and of unichr()
for unicode objects. If a
unicode argument is given and Python was built with UCS2 Unicode, then the
character's code point must be in the range [0..65535] inclusive; otherwise the
string length is two, and a TypeError
will be raised.
pow(x, y[, z])
Return x to the power y; if z is present, return x to the power y,
modulo z (computed more efficiently than pow(x, y) % z
). The two-argument
form pow(x, y)
is equivalent to using the power operator: x**y
.
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, 10**2
returns 100
, but
10**-2
returns 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 z is present, x and y
must be of integer types, and y must be non-negative. (This restriction was
added in Python 2.2. In Python 2.1 and before, floating 3-argument pow()
returned platform-dependent results depending on floating-point rounding
accidents.)
print(*objects, sep=' ', end='\n', file=sys.stdout)
Print objects to the stream file, separated by sep and followed by end. sep, end and file, if present, must be given as keyword arguments.
All non-keyword arguments are converted to strings like str()
does and
written to the stream, separated by sep and followed by end. Both sep
and end must be strings; they can also be None
, which means to use the
default values. If no objects are given, print()
will just write
end.
The file argument must be an object with a write(string)
method; if it
is not present or None
, sys.stdout
will be used. Output buffering
is determined by file. Use file.flush()
to ensure, for instance,
immediate appearance on a screen.
Note
This function is not normally available as a built-in since the name
print
is recognized as the print
statement. To disable the
statement and use the print()
function, use this future statement at
the top of your module:
from __future__ import print_function
New in version 2.6.
class property([fget[, fset[, fdel[, doc]]]])
Return a property attribute for new-style classes (classes that
derive from object
).
fget is a function for getting an attribute value. fset is a function for setting an attribute value. fdel is a function for deleting an attribute value. And doc creates a docstring for the attribute.
A typical use is to define a managed attribute x
:
class C(object):
def __init__(self):
self._x = None
def getx(self):
return self._x
def setx(self, value):
self._x = value
def delx(self):
del self._x
x = property(getx, setx, delx, "I'm the 'x' property.")
If c is an instance of C, c.x
will invoke the getter,
c.x = value
will invoke the setter and del c.x
the deleter.
If given, doc will be the docstring of the property attribute. Otherwise, the
property will copy fget's docstring (if it exists). This makes it possible to
create read-only properties easily using property()
as a decorator:
class Parrot(object):
def __init__(self):
self._voltage = 100000
@property
def voltage(self):
"""Get the current voltage."""
return self._voltage
The @property
decorator turns the voltage()
method into a "getter"
for a read-only attribute with the same name, and it sets the docstring for
voltage to "Get the current voltage."
A property object has getter
, setter
,
and deleter
methods usable as decorators that create a
copy of the property with the corresponding accessor function set to the
decorated function. This is best explained with an example:
class C(object):
def __init__(self):
self._x = None
@property
def x(self):
"""I'm the 'x' property."""
return self._x
@x.setter
def x(self, value):
self._x = value
@x.deleter
def x(self):
del self._x
This code is exactly equivalent to the first example. Be sure to give the
additional functions the same name as the original property (x
in this
case.)
The returned property object also has the attributes fget
, fset
, and
fdel
corresponding to the constructor arguments.
New in version 2.2.
Changed in version 2.5: Use fget's docstring if no doc given.
Changed in version 2.6: The getter
, setter
, and deleter
attributes were added.
range(stop)
range(start, stop[, step])
This is a versatile function to create lists containing arithmetic progressions.
It is most often used in for
loops. The arguments must be plain
integers. If the step argument is omitted, it defaults to 1
. If the
start argument is omitted, it defaults to 0
. The full form returns a list
of plain integers [start, start + step, start + 2 * step, ...]
. If step
is positive, the last element is the largest start + i * step
less than
stop; if step is negative, the last element is the smallest start + i *
step
greater than stop. step must not be zero (or else ValueError
is raised). Example:
raw_input([prompt])
If the 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,
EOFError
is raised. Example:
>>> s = raw_input('--> ')
--> Monty Python's Flying Circus
>>> s
"Monty Python's Flying Circus"
If the readline
module was loaded, then raw_input()
will use it to
provide elaborate line editing and history features.
reduce(function, iterable[, initializer])
Apply function of two arguments cumulatively to the items of iterable, from
left to right, so as to reduce the iterable to a single value. For example,
reduce(lambda x, y: x+y, [1, 2, 3, 4, 5])
calculates ((((1+2)+3)+4)+5)
.
The left argument, x, is the accumulated value and the right argument, y, is
the update value from the iterable. If the optional initializer is present,
it is placed before the items of the iterable in the calculation, and serves as
a default when the iterable is empty. If initializer is not given and
iterable contains only one item, the first item is returned.
Roughly equivalent to:
def reduce(function, iterable, initializer=None):
it = iter(iterable)
if initializer is None:
try:
initializer = next(it)
except StopIteration:
raise TypeError('reduce() of empty sequence with no initial value')
accum_value = initializer
for x in it:
accum_value = function(accum_value, x)
return accum_value
reload(module)
Reload a previously imported 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 module argument).
When reload(module)
is executed:
- Python modules' code is recompiled and the module-level code reexecuted,
defining a new set of objects which are bound to names in the module's
dictionary. The
init
function of extension modules is not called a second time. - As with all other objects in Python the old objects are only reclaimed after their reference counts drop to zero.
- The names in the module namespace are updated to point to any new or changed objects.
- Other references to the old objects (such as names external to the module) are not rebound to refer to the new objects and must be updated in each namespace where they occur if that is desired.
There are a number of other caveats:
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 try
statement it can test
for the table's presence and skip its initialization if desired:
try:
cache
except NameError:
cache = {}
It is generally not very useful to reload built-in or dynamically loaded
modules. Reloading sys
, __main__
, builtins
and other
key modules is not recommended. In many cases 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 from
...
import
..., calling reload()
for the other module does not
redefine the objects imported from it --- one way around this is to re-execute
the from
statement, another is to use import
and qualified
names (module.*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.
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 eval()
, otherwise the
representation is a string enclosed in angle brackets that contains the name
of the type of the object together with additional information often
including the name and address of the object. A class can control what this
function returns for its instances by defining a __repr__()
method.
reversed(seq)
Return a reverse iterator. seq must be an object which has
a __reversed__()
method or supports the sequence protocol (the
__len__()
method and the __getitem__()
method with integer
arguments starting at 0
).
New in version 2.4.
Changed in version 2.6: Added the possibility to write a custom __reversed__()
method.
round(number[, ndigits])
Return the floating point value number rounded to ndigits digits after
the decimal point. If ndigits 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 ndigits; if two multiples are equally close,
rounding is done away from 0 (so, for example, round(0.5)
is 1.0
and
round(-0.5)
is -1.0
).
Note
The behavior of round()
for floats can be surprising: for example,
round(2.675, 2)
gives 2.67
instead of the expected 2.68
.
This is not a bug: it's a result of the fact that most decimal fractions
can't be represented exactly as a float. See Floating Point Arithmetic: Issues and Limitations for
more information.
class set([iterable])
Return a new set
object, optionally with elements taken from
iterable. set
is a built-in class. See set
and
Set Types --- set, frozenset for documentation about this class.
For other containers see the built-in frozenset
, list
,
tuple
, and dict
classes, as well as the collections
module.
New in version 2.4.
setattr(object, name, value)
This is the counterpart of 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, setattr(x, 'foobar', 123)
is equivalent to
x.foobar = 123
.
class slice(stop)
class slice(start, stop[, step])
Return a slice object representing the set of indices specified by
range(start, stop, step)
. The start and step arguments default to
None
. Slice objects have read-only data attributes start
,
stop
and 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. For
example: a[start:stop:step]
or a[start:stop, i]
. See
itertools.islice()
for an alternate version that returns an iterator.
sorted(iterable[, cmp[, key[, reverse]]])
Return a new sorted list from the items in iterable.
The optional arguments cmp, key, and reverse have the same meaning as
those for the list.sort()
method (described in section
Mutable Sequence Types).
cmp specifies a custom comparison function of two arguments (iterable
elements) which should return a negative, zero or positive number depending on
whether the first argument is considered smaller than, equal to, or larger than
the second argument: cmp=lambda x,y: cmp(x.lower(), y.lower())
. The default
value is None
.
key specifies a function of one argument that is used to extract a comparison
key from each list element: key=str.lower
. The default value is None
(compare the elements directly).
reverse is a boolean value. If set to True
, then the list elements are
sorted as if each comparison were reversed.
In general, the key and reverse conversion processes are much faster
than specifying an equivalent cmp function. This is because cmp is
called multiple times for each list element while key and reverse touch
each element only once. Use functools.cmp_to_key()
to convert an
old-style cmp function to a key function.
The built-in sorted()
function is guaranteed to be stable. A sort is
stable if it guarantees not to change the relative order of elements that
compare equal --- this is helpful for sorting in multiple passes (for
example, sort by department, then by salary grade).
For sorting examples and a brief sorting tutorial, see Sorting HOW TO.
New in version 2.4.
staticmethod(function)
Return a static method for function.
A static method does not receive an implicit first argument. To declare a static method, use this idiom:
class C(object):
@staticmethod
def f(arg1, arg2, ...):
...
The @staticmethod
form is a function decorator -- see the
description of function definitions in Function definitions for details.
It can be called either on the class (such as C.f()
) or on an instance (such
as C().f()
). The instance is ignored except for its class.
Static methods in Python are similar to those found in Java or C++. Also see
classmethod()
for a variant that is useful for creating alternate
class constructors.
For more information on static methods, consult the documentation on the standard type hierarchy in The standard type hierarchy.
New in version 2.2.
Changed in version 2.4: Function decorator syntax added.
class str(object='')
Return a string containing a nicely printable representation of an object. For
strings, this returns the string itself. The difference with repr(object)
is that str(object)
does not always attempt to return a string that is
acceptable to eval()
; its goal is to return a printable string. If no
argument is given, returns the empty string, ''
.
For more information on strings see Sequence Types --- str, unicode, list, tuple, bytearray, buffer, xrange which describes sequence
functionality (strings are sequences), and also the string-specific methods
described in the String Methods section. To output formatted strings
use template strings or the %
operator described in the
String Formatting Operations section. In addition see the String Services
section. See also unicode()
.
sum(iterable[, start])
Sums start and the items of an iterable from left to right and returns the
total. start defaults to 0
. The iterable's items are normally numbers,
and the start value is not allowed to be a string.
For some use cases, there are good alternatives to sum()
.
The preferred, fast way to concatenate a sequence of strings is by calling
''.join(sequence)
. To add floating point values with extended precision,
see math.fsum()
. To concatenate a series of iterables, consider using
itertools.chain()
.
New in version 2.3.
super(type[, object-or-type])
Return a proxy object that delegates method calls to a parent or sibling
class of type. This is useful for accessing inherited methods that have
been overridden in a class. The search order is same as that used by
getattr()
except that the type itself is skipped.
The __mro__
attribute of the type lists the method
resolution search order used by both getattr()
and super()
. The
attribute is dynamic and can change whenever the inheritance hierarchy is
updated.
If the second argument is omitted, the super object returned is unbound. If
the second argument is an object, isinstance(obj, type)
must be true. If
the second argument is a type, issubclass(type2, type)
must be true (this
is useful for classmethods).
Note
super()
only works for new-style classes.
There are two typical use cases for super. In a class hierarchy with single inheritance, super can be used to refer to parent classes without naming them explicitly, thus making the code more maintainable. This use closely parallels the use of super in other programming languages.
The second use case is to support cooperative multiple inheritance in a dynamic execution environment. This use case is unique to Python and is not found in statically compiled languages or languages that only support single inheritance. This makes it possible to implement "diamond diagrams" where multiple base classes implement the same method. Good design dictates that this method have the same calling signature in every case (because the order of calls is determined at runtime, because that order adapts to changes in the class hierarchy, and because that order can include sibling classes that are unknown prior to runtime).
For both use cases, a typical superclass call looks like this:
class C(B):
def method(self, arg):
super(C, self).method(arg)
Note that super()
is implemented as part of the binding process for
explicit dotted attribute lookups such as super().__getitem__(name)
.
It does so by implementing its own __getattribute__()
method for searching
classes in a predictable order that supports cooperative multiple inheritance.
Accordingly, super()
is undefined for implicit lookups using statements or
operators such as super()[name]
.
Also note that super()
is not limited to use inside methods. The two
argument form specifies the arguments exactly and makes the appropriate
references.
For practical suggestions on how to design cooperative classes using
super()
, see guide to using super().
New in version 2.2.
tuple([iterable])
Return a tuple whose items are the same and in the same order as iterable's
items. iterable may be a sequence, a container that supports iteration, or an
iterator object. If iterable is already a tuple, it is returned unchanged.
For instance, tuple('abc')
returns ('a', 'b', 'c')
and tuple([1, 2,
3])
returns (1, 2, 3)
. If no argument is given, returns a new empty
tuple, ()
.
tuple
is an immutable sequence type, as documented in
Sequence Types --- str, unicode, list, tuple, bytearray, buffer, xrange. For other containers see the built in dict
,
list
, and set
classes, and the collections
module.
class type(object)
class type(name, bases, dict)
With one argument, return the type of an object. The return value is a
type object. The isinstance()
built-in function is recommended for
testing the type of an object.
With three arguments, return a new type object. This is essentially a
dynamic form of the class
statement. The name string is the
class name and becomes the __name__
attribute; the bases tuple
itemizes the base classes and becomes the __bases__
attribute;
and the dict dictionary is the namespace containing definitions for class
body and becomes the __dict__
attribute. For example, the
following two statements create identical type
objects:
New in version 2.2.
unichr(i)
Return the Unicode string of one character whose Unicode code is the integer
i. For example, unichr(97)
returns the string u'a'
. This is the
inverse of ord()
for Unicode strings. The valid range for the argument
depends how Python was configured -- it may be either UCS2 [0..0xFFFF] or UCS4
[0..0x10FFFF]. ValueError
is raised otherwise. For ASCII and 8-bit
strings see chr()
.
New in version 2.0.
unicode(object='')
unicode(object[, encoding[, errors]])
Return the Unicode string version of object using one of the following modes:
If encoding and/or errors are given, unicode()
will decode the object
which can either be an 8-bit string or a character buffer using the codec for
encoding. The encoding parameter is a string giving the name of an encoding;
if the encoding is not known, LookupError
is raised. Error handling is
done according to errors; this specifies the treatment of characters which are
invalid in the input encoding. If errors is 'strict'
(the default), a
ValueError
is raised on errors, while a value of 'ignore'
causes
errors to be silently ignored, and a value of 'replace'
causes the official
Unicode replacement character, U+FFFD
, to be used to replace input
characters which cannot be decoded. See also the codecs
module.
If no optional parameters are given, unicode()
will mimic the behaviour of
str()
except that it returns Unicode strings instead of 8-bit strings. More
precisely, if object is a Unicode string or subclass it will return that
Unicode string without any additional decoding applied.
For objects which provide a __unicode__()
method, it will call this method
without arguments to create a Unicode string. For all other objects, the 8-bit
string version or representation is requested and then converted to a Unicode
string using the codec for the default encoding in 'strict'
mode.
For more information on Unicode strings see Sequence Types --- str, unicode, list, tuple, bytearray, buffer, xrange which describes
sequence functionality (Unicode strings are sequences), and also the
string-specific methods described in the String Methods section. To
output formatted strings use template strings or the %
operator described
in the String Formatting Operations section. In addition see the
String Services section. See also str()
.
New in version 2.0.
Changed in version 2.2: Support for __unicode__()
added.
vars([object])
Return the __dict__
attribute for a module, class, instance,
or any other object with a __dict__
attribute.
Objects such as modules and instances have an updateable __dict__
attribute; however, other objects may have write restrictions on their
__dict__
attributes (for example, new-style classes use a
dictproxy to prevent direct dictionary updates).
Without an argument, vars()
acts like locals()
. Note, the
locals dictionary is only useful for reads since updates to the locals
dictionary are ignored.
xrange(stop)
xrange(start, stop[, step])
This function is very similar to 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 xrange()
over range()
is minimal (since
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
break
). For more information on xrange objects, see
XRange Type and Sequence Types --- str, unicode, list, tuple, bytearray, buffer, xrange.
CPython implementation detail: xrange()
is intended to be simple and fast. Implementations may
impose restrictions to achieve this. The C implementation of Python
restricts all arguments to native C longs ("short" Python integers), and
also requires that the number of elements fit in a native C long. If a
larger range is needed, an alternate version can be crafted using the
itertools
module: islice(count(start, step),
(stop-start+step-1+2*(step<0))//step)
.
zip([iterable, ...])
This function returns a list of tuples, where the i-th tuple contains the
i-th element from each of the argument sequences or iterables. The returned
list is truncated in length to the length of the shortest argument sequence.
When there are multiple arguments which are all of the same length, zip()
is similar to map()
with an initial argument of None
. With a single
sequence argument, it returns a list of 1-tuples. With no arguments, it returns
an empty list.
The left-to-right evaluation order of the iterables is guaranteed. This
makes possible an idiom for clustering a data series into n-length groups
using zip(*[iter(s)]*n)
.
zip()
in conjunction with the *
operator can be used to unzip a
list:
>>> x = [1, 2, 3]
>>> y = [4, 5, 6]
>>> zipped = zip(x, y)
>>> zipped
[(1, 4), (2, 5), (3, 6)]
>>> x2, y2 = zip(*zipped)
>>> x == list(x2) and y == list(y2)
True
New in version 2.0.
__import__(name[, globals[, locals[, fromlist[, level]]]])
Note
This is an advanced function that is not needed in everyday Python
programming, unlike importlib.import_module()
.
This function is invoked by the import
statement. It can be
replaced (by importing the __builtin__
module and assigning to
__builtin__.__import__
) in order to change semantics of the
import
statement, but nowadays it is usually simpler to use import
hooks (see PEP 302). Direct use of __import__()
is rare, except in
cases where you want to import a module whose name is only known at runtime.
The function imports the module name, potentially using the given globals
and locals to determine how to interpret the name in a package context.
The fromlist gives the names of objects or submodules that should be
imported from the module given by name. The standard implementation does
not use its locals argument at all, and uses its globals only to
determine the package context of the import
statement.
level specifies whether to use absolute or relative imports. The default
is -1
which indicates both absolute and relative imports will be
attempted. 0
means only perform absolute imports. Positive values for
level indicate the number of parent directories to search relative to the
directory of the module calling __import__()
.
When the name variable is of the form package.module
, normally, the
top-level package (the name up till the first dot) is returned, not the
module named by name. However, when a non-empty fromlist argument is
given, the module named by name is returned.
For example, the statement import spam
results in bytecode resembling the
following code:
spam = __import__('spam', globals(), locals(), [], -1)
The statement import spam.ham
results in this call:
spam = __import__('spam.ham', globals(), locals(), [], -1)
Note how __import__()
returns the toplevel module here because this is
the object that is bound to a name by the import
statement.
On the other hand, the statement from spam.ham import eggs, sausage as
saus
results in
_temp = __import__('spam.ham', globals(), locals(), ['eggs', 'sausage'], -1)
eggs = _temp.eggs
saus = _temp.sausage
Here, the spam.ham
module is returned from __import__()
. From this
object, the names to import are retrieved and assigned to their respective
names.
If you simply want to import a module (potentially within a package) by name,
use importlib.import_module()
.
Changed in version 2.5: The level parameter was added.
Changed in version 2.5: Keyword support for parameters was added.
There are several built-in functions that are no longer essential to learn, know or use in modern Python programming. They have been kept here to maintain backwards compatibility with programs written for older versions of Python.
Python programmers, trainers, students and book writers should feel free to bypass these functions without concerns about missing something important.
apply(function, args[, keywords])
The function argument must be a callable object (a user-defined or built-in
function or method, or a class object) and the args argument must be a
sequence. The function is called with args as the argument list; the number
of arguments is the length of the tuple. If the optional 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 argument list. Calling apply()
is
different from just calling function(args)
, since in that case there is
always exactly one argument. The use of apply()
is equivalent to
function(*args, **keywords)
.
Deprecated since version 2.3: Use function(*args, **keywords)
instead of
apply(function, args, keywords)
(see Unpacking Argument Lists).
buffer(object[, offset[, size]])
The object argument must be an object that supports the buffer call interface (such as strings, arrays, and buffers). A new buffer object will be created which references the object argument. The buffer object will be a slice from the beginning of object (or from the specified offset). The slice will extend to the end of object (or will have a length given by the size argument).
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. If coercion is not
possible, raise TypeError
.
intern(string)
Enter string in the table of "interned" strings and return the interned string -- which is 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.
Changed in version 2.3: Interned strings are not immortal (like they used to be in Python 2.2 and
before); you must keep a reference to the return value of intern()
around
to benefit from it.
Footnotes
setvbuf()
. The interface to specify the buffer size is not done using a
method that calls 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.