cpython/Doc/library/operator.rst

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:mod:`operator` --- Standard operators as functions
===================================================
.. module:: operator
:synopsis: Functions corresponding to the standard operators.
.. sectionauthor:: Skip Montanaro <skip@automatrix.com>
.. testsetup::
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import operator
from operator import itemgetter
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The :mod:`operator` module exports a set of functions implemented in C
corresponding to the intrinsic operators of Python. For example,
``operator.add(x, y)`` is equivalent to the expression ``x+y``. The function
names are those used for special class methods; variants without leading and
trailing ``__`` are also provided for convenience.
The functions fall into categories that perform object comparisons, logical
operations, mathematical operations, sequence operations, and abstract type
tests.
The object comparison functions are useful for all objects, and are named after
the rich comparison operators they support:
.. function:: lt(a, b)
le(a, b)
eq(a, b)
ne(a, b)
ge(a, b)
gt(a, b)
__lt__(a, b)
__le__(a, b)
__eq__(a, b)
__ne__(a, b)
__ge__(a, b)
__gt__(a, b)
Perform "rich comparisons" between *a* and *b*. Specifically, ``lt(a, b)`` is
equivalent to ``a < b``, ``le(a, b)`` is equivalent to ``a <= b``, ``eq(a,
b)`` is equivalent to ``a == b``, ``ne(a, b)`` is equivalent to ``a != b``,
``gt(a, b)`` is equivalent to ``a > b`` and ``ge(a, b)`` is equivalent to ``a
>= b``. Note that unlike the built-in :func:`cmp`, these functions can
return any value, which may or may not be interpretable as a Boolean value.
See :ref:`comparisons` for more information about rich comparisons.
.. versionadded:: 2.2
The logical operations are also generally applicable to all objects, and support
truth tests, identity tests, and boolean operations:
.. function:: not_(obj)
__not__(obj)
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Return the outcome of :keyword:`not` *obj*. (Note that there is no
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:meth:`__not__` method for object instances; only the interpreter core defines
this operation. The result is affected by the :meth:`__nonzero__` and
:meth:`__len__` methods.)
.. function:: truth(obj)
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Return :const:`True` if *obj* is true, and :const:`False` otherwise. This is
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equivalent to using the :class:`bool` constructor.
.. function:: is_(a, b)
Return ``a is b``. Tests object identity.
.. versionadded:: 2.3
.. function:: is_not(a, b)
Return ``a is not b``. Tests object identity.
.. versionadded:: 2.3
The mathematical and bitwise operations are the most numerous:
.. function:: abs(obj)
__abs__(obj)
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Return the absolute value of *obj*.
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.. function:: add(a, b)
__add__(a, b)
Return ``a + b``, for *a* and *b* numbers.
.. function:: and_(a, b)
__and__(a, b)
Return the bitwise and of *a* and *b*.
.. function:: div(a, b)
__div__(a, b)
Return ``a / b`` when ``__future__.division`` is not in effect. This is
also known as "classic" division.
.. function:: floordiv(a, b)
__floordiv__(a, b)
Return ``a // b``.
.. versionadded:: 2.2
.. function:: inv(obj)
invert(obj)
__inv__(obj)
__invert__(obj)
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Return the bitwise inverse of the number *obj*. This is equivalent to ``~obj``.
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.. versionadded:: 2.0
The names :func:`invert` and :func:`__invert__`.
.. function:: lshift(a, b)
__lshift__(a, b)
Return *a* shifted left by *b*.
.. function:: mod(a, b)
__mod__(a, b)
Return ``a % b``.
.. function:: mul(a, b)
__mul__(a, b)
Return ``a * b``, for *a* and *b* numbers.
.. function:: neg(obj)
__neg__(obj)
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Return *obj* negated.
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.. function:: or_(a, b)
__or__(a, b)
Return the bitwise or of *a* and *b*.
.. function:: pos(obj)
__pos__(obj)
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Return *obj* positive.
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.. function:: pow(a, b)
__pow__(a, b)
Return ``a ** b``, for *a* and *b* numbers.
.. versionadded:: 2.3
.. function:: rshift(a, b)
__rshift__(a, b)
Return *a* shifted right by *b*.
.. function:: sub(a, b)
__sub__(a, b)
Return ``a - b``.
.. function:: truediv(a, b)
__truediv__(a, b)
Return ``a / b`` when ``__future__.division`` is in effect. This is also
known as "true" division.
.. versionadded:: 2.2
.. function:: xor(a, b)
__xor__(a, b)
Return the bitwise exclusive or of *a* and *b*.
.. function:: index(a)
__index__(a)
Return *a* converted to an integer. Equivalent to ``a.__index__()``.
.. versionadded:: 2.5
Operations which work with sequences include:
.. function:: concat(a, b)
__concat__(a, b)
Return ``a + b`` for *a* and *b* sequences.
.. function:: contains(a, b)
__contains__(a, b)
Return the outcome of the test ``b in a``. Note the reversed operands.
.. versionadded:: 2.0
The name :func:`__contains__`.
.. function:: countOf(a, b)
Return the number of occurrences of *b* in *a*.
.. function:: delitem(a, b)
__delitem__(a, b)
Remove the value of *a* at index *b*.
.. function:: delslice(a, b, c)
__delslice__(a, b, c)
Delete the slice of *a* from index *b* to index *c-1*.
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.. deprecated:: 2.6
This function is removed in Python 3.x. Use :func:`delitem` with a slice
index.
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.. function:: getitem(a, b)
__getitem__(a, b)
Return the value of *a* at index *b*.
.. function:: getslice(a, b, c)
__getslice__(a, b, c)
Return the slice of *a* from index *b* to index *c-1*.
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.. deprecated:: 2.6
This function is removed in Python 3.x. Use :func:`getitem` with a slice
index.
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.. function:: indexOf(a, b)
Return the index of the first of occurrence of *b* in *a*.
.. function:: repeat(a, b)
__repeat__(a, b)
Return ``a * b`` where *a* is a sequence and *b* is an integer.
.. function:: sequenceIncludes(...)
.. deprecated:: 2.0
Use :func:`contains` instead.
Alias for :func:`contains`.
.. function:: setitem(a, b, c)
__setitem__(a, b, c)
Set the value of *a* at index *b* to *c*.
.. function:: setslice(a, b, c, v)
__setslice__(a, b, c, v)
Set the slice of *a* from index *b* to index *c-1* to the sequence *v*.
Merged revisions 67571,67574-67576,67579-67581,67583,67591,67597,67608,67631 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r67571 | georg.brandl | 2008-12-05 10:13:45 +0100 (Fri, 05 Dec 2008) | 2 lines Use markup. ........ r67574 | georg.brandl | 2008-12-05 10:25:32 +0100 (Fri, 05 Dec 2008) | 2 lines #4441 followup: Add link to open() docs for Windows. ........ r67575 | georg.brandl | 2008-12-05 12:34:51 +0100 (Fri, 05 Dec 2008) | 2 lines #4544: add `dedent` to textwrap.__all__. ........ r67576 | georg.brandl | 2008-12-05 13:09:41 +0100 (Fri, 05 Dec 2008) | 2 lines #4529: fix parser's validation for try-except-finally statements. ........ r67579 | georg.brandl | 2008-12-05 16:29:39 +0100 (Fri, 05 Dec 2008) | 2 lines #4517: add "special method" glossary entry and clarify when __getattribute__ is bypassed. ........ r67580 | georg.brandl | 2008-12-05 16:32:29 +0100 (Fri, 05 Dec 2008) | 2 lines #4478: document that copyfile() can raise Error. ........ r67581 | georg.brandl | 2008-12-05 16:42:03 +0100 (Fri, 05 Dec 2008) | 2 lines #3171: document that *slice are removed in 3k. ........ r67583 | georg.brandl | 2008-12-05 16:52:20 +0100 (Fri, 05 Dec 2008) | 4 lines Move __import__ to the bottom of the functions list. It doesn't make sense for such a fundamental document to have the most obscure function listed at the top. ........ r67591 | georg.brandl | 2008-12-05 19:00:06 +0100 (Fri, 05 Dec 2008) | 2 lines Followup to #4511: add link from decorator glossary entry to definition. ........ r67597 | georg.brandl | 2008-12-05 20:03:19 +0100 (Fri, 05 Dec 2008) | 2 lines Remove confusing sentence part. ........ r67608 | georg.brandl | 2008-12-06 12:57:12 +0100 (Sat, 06 Dec 2008) | 2 lines Follow-up to #4488: document PIPE and STDOUT properly. ........ r67631 | georg.brandl | 2008-12-07 12:54:07 +0100 (Sun, 07 Dec 2008) | 2 lines Add link to the favicon to the docs. ........
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.. deprecated:: 2.6
This function is removed in Python 3.x. Use :func:`setitem` with a slice
index.
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Many operations have an "in-place" version. The following functions provide a
more primitive access to in-place operators than the usual syntax does; for
example, the :term:`statement` ``x += y`` is equivalent to
``x = operator.iadd(x, y)``. Another way to put it is to say that
``z = operator.iadd(x, y)`` is equivalent to the compound statement
``z = x; z += y``.
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.. function:: iadd(a, b)
__iadd__(a, b)
``a = iadd(a, b)`` is equivalent to ``a += b``.
.. versionadded:: 2.5
.. function:: iand(a, b)
__iand__(a, b)
``a = iand(a, b)`` is equivalent to ``a &= b``.
.. versionadded:: 2.5
.. function:: iconcat(a, b)
__iconcat__(a, b)
``a = iconcat(a, b)`` is equivalent to ``a += b`` for *a* and *b* sequences.
.. versionadded:: 2.5
.. function:: idiv(a, b)
__idiv__(a, b)
``a = idiv(a, b)`` is equivalent to ``a /= b`` when ``__future__.division`` is
not in effect.
.. versionadded:: 2.5
.. function:: ifloordiv(a, b)
__ifloordiv__(a, b)
``a = ifloordiv(a, b)`` is equivalent to ``a //= b``.
.. versionadded:: 2.5
.. function:: ilshift(a, b)
__ilshift__(a, b)
``a = ilshift(a, b)`` is equivalent to ``a <``\ ``<= b``.
.. versionadded:: 2.5
.. function:: imod(a, b)
__imod__(a, b)
``a = imod(a, b)`` is equivalent to ``a %= b``.
.. versionadded:: 2.5
.. function:: imul(a, b)
__imul__(a, b)
``a = imul(a, b)`` is equivalent to ``a *= b``.
.. versionadded:: 2.5
.. function:: ior(a, b)
__ior__(a, b)
``a = ior(a, b)`` is equivalent to ``a |= b``.
.. versionadded:: 2.5
.. function:: ipow(a, b)
__ipow__(a, b)
``a = ipow(a, b)`` is equivalent to ``a **= b``.
.. versionadded:: 2.5
.. function:: irepeat(a, b)
__irepeat__(a, b)
``a = irepeat(a, b)`` is equivalent to ``a *= b`` where *a* is a sequence and
*b* is an integer.
.. versionadded:: 2.5
.. function:: irshift(a, b)
__irshift__(a, b)
``a = irshift(a, b)`` is equivalent to ``a >>= b``.
.. versionadded:: 2.5
.. function:: isub(a, b)
__isub__(a, b)
``a = isub(a, b)`` is equivalent to ``a -= b``.
.. versionadded:: 2.5
.. function:: itruediv(a, b)
__itruediv__(a, b)
``a = itruediv(a, b)`` is equivalent to ``a /= b`` when ``__future__.division``
is in effect.
.. versionadded:: 2.5
.. function:: ixor(a, b)
__ixor__(a, b)
``a = ixor(a, b)`` is equivalent to ``a ^= b``.
.. versionadded:: 2.5
The :mod:`operator` module also defines a few predicates to test the type of
objects.
.. note::
Be careful not to misinterpret the results of these functions; only
:func:`isCallable` has any measure of reliability with instance objects.
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For example:
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>>> class C:
... pass
Merged revisions 68133-68134,68141-68142,68145-68146,68148-68149,68159-68162,68166,68171-68174,68179,68195-68196,68210,68214-68215,68217-68222 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r68133 | antoine.pitrou | 2009-01-01 16:38:03 +0100 (Thu, 01 Jan 2009) | 1 line fill in actual issue number in tests ........ r68134 | hirokazu.yamamoto | 2009-01-01 16:45:39 +0100 (Thu, 01 Jan 2009) | 2 lines Issue #4797: IOError.filename was not set when _fileio.FileIO failed to open file with `str' filename on Windows. ........ r68141 | benjamin.peterson | 2009-01-01 17:43:12 +0100 (Thu, 01 Jan 2009) | 1 line fix highlighting ........ r68142 | benjamin.peterson | 2009-01-01 18:29:49 +0100 (Thu, 01 Jan 2009) | 2 lines welcome to 2009, Python! ........ r68145 | amaury.forgeotdarc | 2009-01-02 01:03:54 +0100 (Fri, 02 Jan 2009) | 5 lines #4801 _collections module fails to build on cygwin. _PyObject_GC_TRACK is the macro version of PyObject_GC_Track, and according to documentation it should not be used for extension modules. ........ r68146 | ronald.oussoren | 2009-01-02 11:44:46 +0100 (Fri, 02 Jan 2009) | 2 lines Fix for issue4472: "configure --enable-shared doesn't work on OSX" ........ r68148 | ronald.oussoren | 2009-01-02 11:48:31 +0100 (Fri, 02 Jan 2009) | 2 lines Forgot to add a NEWS item in my previous checkin ........ r68149 | ronald.oussoren | 2009-01-02 11:50:48 +0100 (Fri, 02 Jan 2009) | 2 lines Fix for issue4780 ........ r68159 | ronald.oussoren | 2009-01-02 15:48:17 +0100 (Fri, 02 Jan 2009) | 2 lines Fix for issue 1627952 ........ r68160 | ronald.oussoren | 2009-01-02 15:52:09 +0100 (Fri, 02 Jan 2009) | 2 lines Fix for issue r1737832 ........ r68161 | ronald.oussoren | 2009-01-02 16:00:05 +0100 (Fri, 02 Jan 2009) | 3 lines Fix for issue 1149804 ........ r68162 | ronald.oussoren | 2009-01-02 16:06:00 +0100 (Fri, 02 Jan 2009) | 3 lines Fix for issue 4472 is incompatible with Cygwin, this patch should fix that. ........ r68166 | benjamin.peterson | 2009-01-02 19:26:23 +0100 (Fri, 02 Jan 2009) | 1 line document PyMemberDef ........ r68171 | georg.brandl | 2009-01-02 21:25:14 +0100 (Fri, 02 Jan 2009) | 3 lines #4811: fix markup glitches (mostly remains of the conversion), found by Gabriel Genellina. ........ r68172 | martin.v.loewis | 2009-01-02 21:32:55 +0100 (Fri, 02 Jan 2009) | 2 lines Issue #4075: Use OutputDebugStringW in Py_FatalError. ........ r68173 | martin.v.loewis | 2009-01-02 21:40:14 +0100 (Fri, 02 Jan 2009) | 2 lines Issue #4051: Prevent conflict of UNICODE macros in cPickle. ........ r68174 | benjamin.peterson | 2009-01-02 21:47:27 +0100 (Fri, 02 Jan 2009) | 1 line fix compilation on non-Windows platforms ........ r68179 | raymond.hettinger | 2009-01-02 22:26:45 +0100 (Fri, 02 Jan 2009) | 1 line Issue #4615. Document how to use itertools for de-duping. ........ r68195 | georg.brandl | 2009-01-03 14:45:15 +0100 (Sat, 03 Jan 2009) | 2 lines Remove useless string literal. ........ r68196 | georg.brandl | 2009-01-03 15:29:53 +0100 (Sat, 03 Jan 2009) | 2 lines Fix indentation. ........ r68210 | georg.brandl | 2009-01-03 20:10:12 +0100 (Sat, 03 Jan 2009) | 2 lines Set eol-style correctly for mp_distributing.py. ........ r68214 | georg.brandl | 2009-01-03 20:44:48 +0100 (Sat, 03 Jan 2009) | 2 lines Make indentation consistent. ........ r68215 | georg.brandl | 2009-01-03 21:15:14 +0100 (Sat, 03 Jan 2009) | 2 lines Fix role name. ........ r68217 | georg.brandl | 2009-01-03 21:30:15 +0100 (Sat, 03 Jan 2009) | 2 lines Add rstlint, a little tool to find subtle markup problems and inconsistencies in the Doc sources. ........ r68218 | georg.brandl | 2009-01-03 21:38:59 +0100 (Sat, 03 Jan 2009) | 2 lines Recognize usage of the default role. ........ r68219 | georg.brandl | 2009-01-03 21:47:01 +0100 (Sat, 03 Jan 2009) | 2 lines Fix uses of the default role. ........ r68220 | georg.brandl | 2009-01-03 21:55:06 +0100 (Sat, 03 Jan 2009) | 2 lines Remove trailing whitespace. ........ r68221 | georg.brandl | 2009-01-03 22:04:55 +0100 (Sat, 03 Jan 2009) | 2 lines Remove tabs from the documentation. ........ r68222 | georg.brandl | 2009-01-03 22:11:58 +0100 (Sat, 03 Jan 2009) | 2 lines Disable the line length checker by default. ........
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...
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>>> import operator
>>> obj = C()
>>> operator.isMappingType(obj)
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True
.. note::
Python 3 is expected to introduce abstract base classes for
collection types, so it should be possible to write, for example,
``isinstance(obj, collections.Mapping)`` and ``isinstance(obj,
collections.Sequence)``.
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.. function:: isCallable(obj)
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.. deprecated:: 2.0
Use the :func:`callable` built-in function instead.
Returns true if the object *obj* can be called like a function, otherwise it
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returns false. True is returned for functions, bound and unbound methods, class
objects, and instance objects which support the :meth:`__call__` method.
.. function:: isMappingType(obj)
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Returns true if the object *obj* supports the mapping interface. This is true for
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dictionaries and all instance objects defining :meth:`__getitem__`.
.. warning::
There is no reliable way to test if an instance supports the complete mapping
protocol since the interface itself is ill-defined. This makes this test less
useful than it otherwise might be.
.. function:: isNumberType(obj)
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Returns true if the object *obj* represents a number. This is true for all
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numeric types implemented in C.
.. warning::
There is no reliable way to test if an instance supports the complete numeric
interface since the interface itself is ill-defined. This makes this test less
useful than it otherwise might be.
.. function:: isSequenceType(obj)
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Returns true if the object *obj* supports the sequence protocol. This returns true
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for all objects which define sequence methods in C, and for all instance objects
defining :meth:`__getitem__`.
.. warning::
There is no reliable way to test if an instance supports the complete sequence
interface since the interface itself is ill-defined. This makes this test less
useful than it otherwise might be.
Example: Build a dictionary that maps the ordinals from ``0`` to ``255`` to
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their character equivalents.
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>>> d = {}
>>> keys = range(256)
>>> vals = map(chr, keys)
>>> map(operator.setitem, [d]*len(keys), keys, vals) # doctest: +SKIP
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.. XXX: find a better, readable, example
The :mod:`operator` module also defines tools for generalized attribute and item
lookups. These are useful for making fast field extractors as arguments for
:func:`map`, :func:`sorted`, :meth:`itertools.groupby`, or other functions that
expect a function argument.
.. function:: attrgetter(attr[, args...])
Return a callable object that fetches *attr* from its operand. If more than one
attribute is requested, returns a tuple of attributes. After,
``f = attrgetter('name')``, the call ``f(b)`` returns ``b.name``. After,
``f = attrgetter('name', 'date')``, the call ``f(b)`` returns ``(b.name,
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b.date)``.
The attribute names can also contain dots; after ``f = attrgetter('date.month')``,
the call ``f(b)`` returns ``b.date.month``.
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.. versionadded:: 2.4
.. versionchanged:: 2.5
Added support for multiple attributes.
.. versionchanged:: 2.6
Added support for dotted attributes.
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.. function:: itemgetter(item[, args...])
Return a callable object that fetches *item* from its operand using the
operand's :meth:`__getitem__` method. If multiple items are specified,
returns a tuple of lookup values. Equivalent to::
def itemgetter(*items):
if len(items) == 1:
item = items[0]
def g(obj):
return obj[item]
else:
def g(obj):
return tuple(obj[item] for item in items)
return g
Merged revisions 68133-68134,68141-68142,68145-68146,68148-68149,68159-68162,68166,68171-68174,68179,68195-68196,68210,68214-68215,68217-68222 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r68133 | antoine.pitrou | 2009-01-01 16:38:03 +0100 (Thu, 01 Jan 2009) | 1 line fill in actual issue number in tests ........ r68134 | hirokazu.yamamoto | 2009-01-01 16:45:39 +0100 (Thu, 01 Jan 2009) | 2 lines Issue #4797: IOError.filename was not set when _fileio.FileIO failed to open file with `str' filename on Windows. ........ r68141 | benjamin.peterson | 2009-01-01 17:43:12 +0100 (Thu, 01 Jan 2009) | 1 line fix highlighting ........ r68142 | benjamin.peterson | 2009-01-01 18:29:49 +0100 (Thu, 01 Jan 2009) | 2 lines welcome to 2009, Python! ........ r68145 | amaury.forgeotdarc | 2009-01-02 01:03:54 +0100 (Fri, 02 Jan 2009) | 5 lines #4801 _collections module fails to build on cygwin. _PyObject_GC_TRACK is the macro version of PyObject_GC_Track, and according to documentation it should not be used for extension modules. ........ r68146 | ronald.oussoren | 2009-01-02 11:44:46 +0100 (Fri, 02 Jan 2009) | 2 lines Fix for issue4472: "configure --enable-shared doesn't work on OSX" ........ r68148 | ronald.oussoren | 2009-01-02 11:48:31 +0100 (Fri, 02 Jan 2009) | 2 lines Forgot to add a NEWS item in my previous checkin ........ r68149 | ronald.oussoren | 2009-01-02 11:50:48 +0100 (Fri, 02 Jan 2009) | 2 lines Fix for issue4780 ........ r68159 | ronald.oussoren | 2009-01-02 15:48:17 +0100 (Fri, 02 Jan 2009) | 2 lines Fix for issue 1627952 ........ r68160 | ronald.oussoren | 2009-01-02 15:52:09 +0100 (Fri, 02 Jan 2009) | 2 lines Fix for issue r1737832 ........ r68161 | ronald.oussoren | 2009-01-02 16:00:05 +0100 (Fri, 02 Jan 2009) | 3 lines Fix for issue 1149804 ........ r68162 | ronald.oussoren | 2009-01-02 16:06:00 +0100 (Fri, 02 Jan 2009) | 3 lines Fix for issue 4472 is incompatible with Cygwin, this patch should fix that. ........ r68166 | benjamin.peterson | 2009-01-02 19:26:23 +0100 (Fri, 02 Jan 2009) | 1 line document PyMemberDef ........ r68171 | georg.brandl | 2009-01-02 21:25:14 +0100 (Fri, 02 Jan 2009) | 3 lines #4811: fix markup glitches (mostly remains of the conversion), found by Gabriel Genellina. ........ r68172 | martin.v.loewis | 2009-01-02 21:32:55 +0100 (Fri, 02 Jan 2009) | 2 lines Issue #4075: Use OutputDebugStringW in Py_FatalError. ........ r68173 | martin.v.loewis | 2009-01-02 21:40:14 +0100 (Fri, 02 Jan 2009) | 2 lines Issue #4051: Prevent conflict of UNICODE macros in cPickle. ........ r68174 | benjamin.peterson | 2009-01-02 21:47:27 +0100 (Fri, 02 Jan 2009) | 1 line fix compilation on non-Windows platforms ........ r68179 | raymond.hettinger | 2009-01-02 22:26:45 +0100 (Fri, 02 Jan 2009) | 1 line Issue #4615. Document how to use itertools for de-duping. ........ r68195 | georg.brandl | 2009-01-03 14:45:15 +0100 (Sat, 03 Jan 2009) | 2 lines Remove useless string literal. ........ r68196 | georg.brandl | 2009-01-03 15:29:53 +0100 (Sat, 03 Jan 2009) | 2 lines Fix indentation. ........ r68210 | georg.brandl | 2009-01-03 20:10:12 +0100 (Sat, 03 Jan 2009) | 2 lines Set eol-style correctly for mp_distributing.py. ........ r68214 | georg.brandl | 2009-01-03 20:44:48 +0100 (Sat, 03 Jan 2009) | 2 lines Make indentation consistent. ........ r68215 | georg.brandl | 2009-01-03 21:15:14 +0100 (Sat, 03 Jan 2009) | 2 lines Fix role name. ........ r68217 | georg.brandl | 2009-01-03 21:30:15 +0100 (Sat, 03 Jan 2009) | 2 lines Add rstlint, a little tool to find subtle markup problems and inconsistencies in the Doc sources. ........ r68218 | georg.brandl | 2009-01-03 21:38:59 +0100 (Sat, 03 Jan 2009) | 2 lines Recognize usage of the default role. ........ r68219 | georg.brandl | 2009-01-03 21:47:01 +0100 (Sat, 03 Jan 2009) | 2 lines Fix uses of the default role. ........ r68220 | georg.brandl | 2009-01-03 21:55:06 +0100 (Sat, 03 Jan 2009) | 2 lines Remove trailing whitespace. ........ r68221 | georg.brandl | 2009-01-03 22:04:55 +0100 (Sat, 03 Jan 2009) | 2 lines Remove tabs from the documentation. ........ r68222 | georg.brandl | 2009-01-03 22:11:58 +0100 (Sat, 03 Jan 2009) | 2 lines Disable the line length checker by default. ........
2009-01-03 17:55:17 -04:00
The items can be any type accepted by the operand's :meth:`__getitem__`
method. Dictionaries accept any hashable value. Lists, tuples, and
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strings accept an index or a slice:
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>>> itemgetter(1)('ABCDEFG')
'B'
>>> itemgetter(1,3,5)('ABCDEFG')
('B', 'D', 'F')
>>> itemgetter(slice(2,None))('ABCDEFG')
'CDEFG'
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.. versionadded:: 2.4
.. versionchanged:: 2.5
Added support for multiple item extraction.
Example of using :func:`itemgetter` to retrieve specific fields from a
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tuple record:
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>>> inventory = [('apple', 3), ('banana', 2), ('pear', 5), ('orange', 1)]
>>> getcount = itemgetter(1)
>>> map(getcount, inventory)
[3, 2, 5, 1]
>>> sorted(inventory, key=getcount)
[('orange', 1), ('banana', 2), ('apple', 3), ('pear', 5)]
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.. function:: methodcaller(name[, args...])
Return a callable object that calls the method *name* on its operand. If
additional arguments and/or keyword arguments are given, they will be given
to the method as well. After ``f = methodcaller('name')``, the call ``f(b)``
returns ``b.name()``. After ``f = methodcaller('name', 'foo', bar=1)``, the
call ``f(b)`` returns ``b.name('foo', bar=1)``.
.. versionadded:: 2.6
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.. _operator-map:
Mapping Operators to Functions
------------------------------
This table shows how abstract operations correspond to operator symbols in the
Python syntax and the functions in the :mod:`operator` module.
+-----------------------+-------------------------+---------------------------------+
| Operation | Syntax | Function |
+=======================+=========================+=================================+
| Addition | ``a + b`` | ``add(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Concatenation | ``seq1 + seq2`` | ``concat(seq1, seq2)`` |
+-----------------------+-------------------------+---------------------------------+
| Containment Test | ``obj in seq`` | ``contains(seq, obj)`` |
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+-----------------------+-------------------------+---------------------------------+
| Division | ``a / b`` | ``div(a, b)`` (without |
| | | ``__future__.division``) |
+-----------------------+-------------------------+---------------------------------+
| Division | ``a / b`` | ``truediv(a, b)`` (with |
| | | ``__future__.division``) |
+-----------------------+-------------------------+---------------------------------+
| Division | ``a // b`` | ``floordiv(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Bitwise And | ``a & b`` | ``and_(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Bitwise Exclusive Or | ``a ^ b`` | ``xor(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Bitwise Inversion | ``~ a`` | ``invert(a)`` |
+-----------------------+-------------------------+---------------------------------+
| Bitwise Or | ``a | b`` | ``or_(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Exponentiation | ``a ** b`` | ``pow(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Identity | ``a is b`` | ``is_(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Identity | ``a is not b`` | ``is_not(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Indexed Assignment | ``obj[k] = v`` | ``setitem(obj, k, v)`` |
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+-----------------------+-------------------------+---------------------------------+
| Indexed Deletion | ``del obj[k]`` | ``delitem(obj, k)`` |
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+-----------------------+-------------------------+---------------------------------+
| Indexing | ``obj[k]`` | ``getitem(obj, k)`` |
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+-----------------------+-------------------------+---------------------------------+
| Left Shift | ``a << b`` | ``lshift(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Modulo | ``a % b`` | ``mod(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Multiplication | ``a * b`` | ``mul(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Negation (Arithmetic) | ``- a`` | ``neg(a)`` |
+-----------------------+-------------------------+---------------------------------+
| Negation (Logical) | ``not a`` | ``not_(a)`` |
+-----------------------+-------------------------+---------------------------------+
| Right Shift | ``a >> b`` | ``rshift(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
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| Sequence Repetition | ``seq * i`` | ``repeat(seq, i)`` |
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+-----------------------+-------------------------+---------------------------------+
| Slice Assignment | ``seq[i:j] = values`` | ``setslice(seq, i, j, values)`` |
+-----------------------+-------------------------+---------------------------------+
| Slice Deletion | ``del seq[i:j]`` | ``delslice(seq, i, j)`` |
+-----------------------+-------------------------+---------------------------------+
| Slicing | ``seq[i:j]`` | ``getslice(seq, i, j)`` |
+-----------------------+-------------------------+---------------------------------+
| String Formatting | ``s % obj`` | ``mod(s, obj)`` |
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+-----------------------+-------------------------+---------------------------------+
| Subtraction | ``a - b`` | ``sub(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Truth Test | ``obj`` | ``truth(obj)`` |
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+-----------------------+-------------------------+---------------------------------+
| Ordering | ``a < b`` | ``lt(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Ordering | ``a <= b`` | ``le(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Equality | ``a == b`` | ``eq(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Difference | ``a != b`` | ``ne(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Ordering | ``a >= b`` | ``ge(a, b)`` |
+-----------------------+-------------------------+---------------------------------+
| Ordering | ``a > b`` | ``gt(a, b)`` |
+-----------------------+-------------------------+---------------------------------+