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Python Library Reference |  |
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Python Library Reference | |
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The 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:
| a, b) |
| a, b) |
| a, b) |
| a, b) |
| a, b) |
| a, b) |
| a, b) |
| a, b) |
| a, b) |
| a, b) |
| a, b) |
| a, b) |
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 cmp(), these functions can
return any value, which may or may not be interpretable as a Boolean
value. See the Python Reference Manual
for more informations about rich comparisons.
New in version 2.2.
The logical operations are also generally applicable to all objects, and support truth tests, identity tests, and boolean operations:
| o) |
| o) |
| o) |
The mathematical and bitwise operations are the most numerous:
| a, b) |
| a, b) |
/ b when __future__.division is not
in effect. This is also known as ``classic'' division.
| o) |
| o) |
| o) |
| o) |
~o. The names invert() and
__invert__() were added in Python 2.0.
| a, b) |
| a, b) |
/ b when __future__.division is in
effect. This is also known as division.
New in version 2.2.
Operations which work with sequences include:
| a, b) |
| a, b) |
in a.
Note the reversed operands. The name __contains__() was
added in Python 2.0.
| a, b, c, v) |
| a, b, c, v) |
-1 to the
sequence v.
The 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 isCallable() has any measure of reliability with instance objects. For example:
>>> class C: ... pass ... >>> import operator >>> o = C() >>> operator.isMappingType(o) True
| o) |
| o) |
| o) |
| o) |
Example: Build a dictionary that maps the ordinals from 0 to
256 to their character equivalents.
>>> import operator
>>> d = {}
>>> keys = range(256)
>>> vals = map(chr, keys)
>>> map(operator.setitem, [d]*len(keys), keys, vals)
The operator module also defines tools for generalized attribute and item lookups. These are useful for making fast field extractors as arguments for map(), sorted(), itertools.groupby(), or other functions that expect a function argument.
| attr) |
| item) |
Examples:
>>> from operator import *
>>> 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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Python Library Reference | |
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