619 lines
19 KiB
ReStructuredText
619 lines
19 KiB
ReStructuredText
:mod:`operator` --- Standard operators as functions
|
|
===================================================
|
|
|
|
.. module:: operator
|
|
:synopsis: Functions corresponding to the standard operators.
|
|
.. sectionauthor:: Skip Montanaro <skip@automatrix.com>
|
|
|
|
|
|
|
|
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)
|
|
|
|
Return the outcome of :keyword:`not` *obj*. (Note that there is no
|
|
: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)
|
|
|
|
Return :const:`True` if *obj* is true, and :const:`False` otherwise. This is
|
|
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)
|
|
|
|
Return the absolute value of *obj*.
|
|
|
|
|
|
.. 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)
|
|
|
|
Return the bitwise inverse of the number *obj*. This is equivalent to ``~obj``.
|
|
|
|
.. 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)
|
|
|
|
Return *obj* negated.
|
|
|
|
|
|
.. function:: or_(a, b)
|
|
__or__(a, b)
|
|
|
|
Return the bitwise or of *a* and *b*.
|
|
|
|
|
|
.. function:: pos(obj)
|
|
__pos__(obj)
|
|
|
|
Return *obj* positive.
|
|
|
|
|
|
.. 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*.
|
|
|
|
|
|
.. 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*.
|
|
|
|
|
|
.. 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*.
|
|
|
|
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 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``.
|
|
|
|
|
|
.. 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.
|
|
For example::
|
|
|
|
>>> class C:
|
|
... pass
|
|
...
|
|
>>> import operator
|
|
>>> obj = C()
|
|
>>> operator.isMappingType(obj)
|
|
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)``.
|
|
|
|
.. function:: isCallable(obj)
|
|
|
|
.. 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
|
|
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)
|
|
|
|
Returns true if the object *obj* supports the mapping interface. This is true for
|
|
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)
|
|
|
|
Returns true if the object *obj* represents a number. This is true for all
|
|
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)
|
|
|
|
Returns true if the object *obj* supports the sequence protocol. This returns true
|
|
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
|
|
their character equivalents. ::
|
|
|
|
>>> import operator
|
|
>>> d = {}
|
|
>>> keys = range(256)
|
|
>>> vals = map(chr, keys)
|
|
>>> map(operator.setitem, [d]*len(keys), keys, vals)
|
|
|
|
.. 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,
|
|
b.date)``.
|
|
|
|
.. versionadded:: 2.4
|
|
|
|
.. versionchanged:: 2.5
|
|
Added support for multiple attributes.
|
|
|
|
|
|
.. function:: itemgetter(item[, args...])
|
|
|
|
Return a callable object that fetches *item* from its operand. If more than one
|
|
item is requested, returns a tuple of items. After, ``f=itemgetter(2)``, the
|
|
call ``f(b)`` returns ``b[2]``. After, ``f=itemgetter(2,5,3)``, the call
|
|
``f(b)`` returns ``(b[2], b[5], b[3])``.
|
|
|
|
.. versionadded:: 2.4
|
|
|
|
.. versionchanged:: 2.5
|
|
Added support for multiple item extraction.
|
|
|
|
Examples::
|
|
|
|
>>> from operator import itemgetter
|
|
>>> 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)]
|
|
|
|
|
|
.. _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)`` |
|
|
+-----------------------+-------------------------+---------------------------------+
|
|
| 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)`` |
|
|
+-----------------------+-------------------------+---------------------------------+
|
|
| Indexed Deletion | ``del obj[k]`` | ``delitem(obj, k)`` |
|
|
+-----------------------+-------------------------+---------------------------------+
|
|
| Indexing | ``obj[k]`` | ``getitem(obj, k)`` |
|
|
+-----------------------+-------------------------+---------------------------------+
|
|
| 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)`` |
|
|
+-----------------------+-------------------------+---------------------------------+
|
|
| Sequence Repitition | ``seq * i`` | ``repeat(seq, i)`` |
|
|
+-----------------------+-------------------------+---------------------------------+
|
|
| 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)`` |
|
|
+-----------------------+-------------------------+---------------------------------+
|
|
| Subtraction | ``a - b`` | ``sub(a, b)`` |
|
|
+-----------------------+-------------------------+---------------------------------+
|
|
| Truth Test | ``obj`` | ``truth(obj)`` |
|
|
+-----------------------+-------------------------+---------------------------------+
|
|
| 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)`` |
|
|
+-----------------------+-------------------------+---------------------------------+
|
|
|