mirror of
https://github.com/python/cpython.git
synced 2024-12-12 19:33:52 +08:00
515 lines
18 KiB
ReStructuredText
515 lines
18 KiB
ReStructuredText
:mod:`operator` --- Standard operators as functions
|
|
===================================================
|
|
|
|
.. module:: operator
|
|
:synopsis: Functions corresponding to the standard operators.
|
|
.. sectionauthor:: Skip Montanaro <skip@automatrix.com>
|
|
|
|
|
|
.. testsetup::
|
|
|
|
import operator
|
|
from operator import itemgetter, iadd
|
|
|
|
|
|
The :mod:`operator` module exports a set of efficient functions 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 and sequence operations.
|
|
|
|
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 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.
|
|
|
|
|
|
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:`__bool__` 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.
|
|
|
|
|
|
.. function:: is_not(a, b)
|
|
|
|
Return ``a is not b``. Tests object identity.
|
|
|
|
|
|
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:: floordiv(a, b)
|
|
__floordiv__(a, b)
|
|
|
|
Return ``a // b``.
|
|
|
|
|
|
.. function:: index(a)
|
|
__index__(a)
|
|
|
|
Return *a* converted to an integer. Equivalent to ``a.__index__()``.
|
|
|
|
|
|
.. function:: inv(obj)
|
|
invert(obj)
|
|
__inv__(obj)
|
|
__invert__(obj)
|
|
|
|
Return the bitwise inverse of the number *obj*. This is equivalent to ``~obj``.
|
|
|
|
|
|
.. 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 (``-obj``).
|
|
|
|
|
|
.. function:: or_(a, b)
|
|
__or__(a, b)
|
|
|
|
Return the bitwise or of *a* and *b*.
|
|
|
|
|
|
.. function:: pos(obj)
|
|
__pos__(obj)
|
|
|
|
Return *obj* positive (``+obj``).
|
|
|
|
|
|
.. function:: pow(a, b)
|
|
__pow__(a, b)
|
|
|
|
Return ``a ** b``, for *a* and *b* numbers.
|
|
|
|
|
|
.. 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`` where 2/3 is .66 rather than 0. This is also known as
|
|
"true" division.
|
|
|
|
|
|
.. function:: xor(a, b)
|
|
__xor__(a, b)
|
|
|
|
Return the bitwise exclusive or of *a* and *b*.
|
|
|
|
|
|
Operations which work with sequences (some of them with mappings too) 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.
|
|
|
|
|
|
.. 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:: getitem(a, b)
|
|
__getitem__(a, b)
|
|
|
|
Return the value of *a* at index *b*.
|
|
|
|
|
|
.. function:: indexOf(a, b)
|
|
|
|
Return the index of the first of occurrence of *b* in *a*.
|
|
|
|
|
|
.. function:: setitem(a, b, c)
|
|
__setitem__(a, b, c)
|
|
|
|
Set the value of *a* at index *b* to *c*.
|
|
|
|
Example: Build a dictionary that maps the ordinals from ``0`` to ``255`` to
|
|
their character equivalents.
|
|
|
|
>>> d = {}
|
|
>>> keys = range(256)
|
|
>>> vals = map(chr, keys)
|
|
>>> map(operator.setitem, [d]*len(keys), keys, vals) # doctest: +SKIP
|
|
|
|
.. 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)``. Equivalent to::
|
|
|
|
def attrgetter(*items):
|
|
if any(not isinstance(item, str) for item in items):
|
|
raise TypeError('attribute name must be a string')
|
|
if len(items) == 1:
|
|
attr = items[0]
|
|
def g(obj):
|
|
return resolve_attr(obj, attr)
|
|
else:
|
|
def g(obj):
|
|
return tuple(resolve_att(obj, attr) for attr in items)
|
|
return g
|
|
|
|
def resolve_attr(obj, attr):
|
|
for name in attr.split("."):
|
|
obj = getattr(obj, name)
|
|
return obj
|
|
|
|
|
|
The attribute names can also contain dots; after ``f = attrgetter('date.month')``,
|
|
the call ``f(b)`` returns ``b.date.month``.
|
|
|
|
.. 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
|
|
|
|
The items can be any type accepted by the operand's :meth:`__getitem__`
|
|
method. Dictionaries accept any hashable value. Lists, tuples, and
|
|
strings accept an index or a slice:
|
|
|
|
>>> itemgetter(1)('ABCDEFG')
|
|
'B'
|
|
>>> itemgetter(1,3,5)('ABCDEFG')
|
|
('B', 'D', 'F')
|
|
>>> itemgetter(slice(2,None))('ABCDEFG')
|
|
'CDEFG'
|
|
|
|
|
|
Example of using :func:`itemgetter` to retrieve specific fields from a
|
|
tuple record:
|
|
|
|
>>> inventory = [('apple', 3), ('banana', 2), ('pear', 5), ('orange', 1)]
|
|
>>> getcount = itemgetter(1)
|
|
>>> list(map(getcount, inventory))
|
|
[3, 2, 5, 1]
|
|
>>> sorted(inventory, key=getcount)
|
|
[('orange', 1), ('banana', 2), ('apple', 3), ('pear', 5)]
|
|
|
|
|
|
.. 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)``. Equivalent to::
|
|
|
|
def methodcaller(name, *args, **kwargs):
|
|
def caller(obj):
|
|
return getattr(obj, name)(*args, **kwargs)
|
|
return caller
|
|
|
|
|
|
.. _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`` | ``truediv(a, b)`` |
|
|
+-----------------------+-------------------------+---------------------------------------+
|
|
| 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)`` |
|
|
+-----------------------+-------------------------+---------------------------------------+
|
|
| Positive | ``+ a`` | ``pos(a)`` |
|
|
+-----------------------+-------------------------+---------------------------------------+
|
|
| Right Shift | ``a >> b`` | ``rshift(a, b)`` |
|
|
+-----------------------+-------------------------+---------------------------------------+
|
|
| Slice Assignment | ``seq[i:j] = values`` | ``setitem(seq, slice(i, j), values)`` |
|
|
+-----------------------+-------------------------+---------------------------------------+
|
|
| Slice Deletion | ``del seq[i:j]`` | ``delitem(seq, slice(i, j))`` |
|
|
+-----------------------+-------------------------+---------------------------------------+
|
|
| Slicing | ``seq[i:j]`` | ``getitem(seq, slice(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)`` |
|
|
+-----------------------+-------------------------+---------------------------------------+
|
|
|
|
Inplace Operators
|
|
-----------------
|
|
|
|
Many operations have an "in-place" version. Listed below are functions
|
|
providing 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``.
|
|
|
|
In those examples, note that when an in-place method is called, the computation
|
|
and assignment are performed in two separate steps. The in-place functions
|
|
listed below only do the first step, calling the in-place method. The second
|
|
step, assignment, is not handled.
|
|
|
|
For immutable targets such as strings, numbers, and tuples, the updated
|
|
value is computed, but not assigned back to the input variable:
|
|
|
|
>>> a = 'hello'
|
|
>>> iadd(a, ' world')
|
|
'hello world'
|
|
>>> a
|
|
'hello'
|
|
|
|
For mutable targets such as lists and dictionaries, the inplace method
|
|
will perform the update, so no subsequent assignment is necessary:
|
|
|
|
>>> s = ['h', 'e', 'l', 'l', 'o']
|
|
>>> iadd(s, [' ', 'w', 'o', 'r', 'l', 'd'])
|
|
['h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd']
|
|
>>> s
|
|
['h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd']
|
|
|
|
.. function:: iadd(a, b)
|
|
__iadd__(a, b)
|
|
|
|
``a = iadd(a, b)`` is equivalent to ``a += b``.
|
|
|
|
|
|
.. function:: iand(a, b)
|
|
__iand__(a, b)
|
|
|
|
``a = iand(a, b)`` is equivalent to ``a &= b``.
|
|
|
|
|
|
.. function:: iconcat(a, b)
|
|
__iconcat__(a, b)
|
|
|
|
``a = iconcat(a, b)`` is equivalent to ``a += b`` for *a* and *b* sequences.
|
|
|
|
|
|
.. function:: ifloordiv(a, b)
|
|
__ifloordiv__(a, b)
|
|
|
|
``a = ifloordiv(a, b)`` is equivalent to ``a //= b``.
|
|
|
|
|
|
.. function:: ilshift(a, b)
|
|
__ilshift__(a, b)
|
|
|
|
``a = ilshift(a, b)`` is equivalent to ``a <<= b``.
|
|
|
|
|
|
.. function:: imod(a, b)
|
|
__imod__(a, b)
|
|
|
|
``a = imod(a, b)`` is equivalent to ``a %= b``.
|
|
|
|
|
|
.. function:: imul(a, b)
|
|
__imul__(a, b)
|
|
|
|
``a = imul(a, b)`` is equivalent to ``a *= b``.
|
|
|
|
|
|
.. function:: ior(a, b)
|
|
__ior__(a, b)
|
|
|
|
``a = ior(a, b)`` is equivalent to ``a |= b``.
|
|
|
|
|
|
.. function:: ipow(a, b)
|
|
__ipow__(a, b)
|
|
|
|
``a = ipow(a, b)`` is equivalent to ``a **= b``.
|
|
|
|
|
|
.. function:: irshift(a, b)
|
|
__irshift__(a, b)
|
|
|
|
``a = irshift(a, b)`` is equivalent to ``a >>= b``.
|
|
|
|
|
|
.. function:: isub(a, b)
|
|
__isub__(a, b)
|
|
|
|
``a = isub(a, b)`` is equivalent to ``a -= b``.
|
|
|
|
|
|
.. function:: itruediv(a, b)
|
|
__itruediv__(a, b)
|
|
|
|
``a = itruediv(a, b)`` is equivalent to ``a /= b``.
|
|
|
|
|
|
.. function:: ixor(a, b)
|
|
__ixor__(a, b)
|
|
|
|
``a = ixor(a, b)`` is equivalent to ``a ^= b``.
|