python operator module

简介

operator模块提供了一套与Python的内置运算符对应的高效率函数。 许多函数名与特殊方法名相同，只是没有双下划线。为了向后兼容性，也保留了许多包含双下划线的函数。为了表述清楚，建议使用没有双下划线的函数。

函数包含的种类有：对象的比较运算、逻辑运算、数学运算以及序列运算。

源代码: Lib/operator.py

>>> import operator
>>> dir(operator)
	       
['__abs__', '__add__', '__all__', '__and__', '__builtins__', '__cached__', '__concat__', '__contains__', '__delitem__', '__doc__', '__eq__', '__file__', '__floordiv__', '__ge__', '__getitem__', '__gt__', '__iadd__', '__iand__', '__iconcat__', '__ifloordiv__', '__ilshift__', '__imatmul__', '__imod__', '__imul__', '__index__', '__inv__', '__invert__', '__ior__', '__ipow__', '__irshift__', '__isub__', '__itruediv__', '__ixor__', '__le__', '__loader__', '__lshift__', '__lt__', '__matmul__', '__mod__', '__mul__', '__name__', '__ne__', '__neg__', '__not__', '__or__', '__package__', '__pos__', '__pow__', '__rshift__', '__setitem__', '__spec__', '__sub__', '__truediv__', '__xor__', '_abs', 'abs', 'add', 'and_', 'attrgetter', 'concat', 'contains', 'countOf', 'delitem', 'eq', 'floordiv', 'ge', 'getitem', 'gt', 'iadd', 'iand', 'iconcat', 'ifloordiv', 'ilshift', 'imatmul', 'imod', 'imul', 'index', 'indexOf', 'inv', 'invert', 'ior', 'ipow', 'irshift', 'is_', 'is_not', 'isub', 'itemgetter', 'itruediv', 'ixor', 'le', 'length_hint', 'lshift', 'lt', 'matmul', 'methodcaller', 'mod', 'mul', 'ne', 'neg', 'not_', 'or_', 'pos', 'pow', 'rshift', 'setitem', 'sub', 'truediv', 'truth', 'xor']

对象比较函数

对象比较函数适用于所有的对象，函数名根据它们对应的比较运算符命名。

operator.lt(a, b)			# a < b
operator.le(a, b)			# a <= b
operator.eq(a, b)			# a == b
operator.ne(a, b)			# a != b
operator.ge(a, b)			# a >= b
operator.gt(a, b)			# a > b

operator.__lt__(a, b)		# a < b
operator.__le__(a, b)		# a <= b
operator.__eq__(a, b)		# a == b
operator.__ne__(a, b)		# a != b
operator.__ge__(a, b)		# a >= b
operator.__gt__(a, b)		# a > b

逻辑运算

operator.not_(obj)
operator.__not__(obj)
	Return the outcome of not obj. 

operator.truth(obj)
	Return True if obj is true, and False otherwise. This is equivalent to using the bool constructor.

operator.is_(a, b)
	Return a is b. Tests object identity.

operator.is_not(a, b)
	Return a is not b. Tests object identity.

赋值运算

operator.iadd(a, b)
operator.__iadd__(a, b)
	a = iadd(a, b) is equivalent to a += b.

operator.iand(a, b)
operator.__iand__(a, b)
	a = iand(a, b) is equivalent to a &= b.

operator.iconcat(a, b)
operator.__iconcat__(a, b)
	a = iconcat(a, b) is equivalent to a += b for a and b sequences.

operator.ifloordiv(a, b)
operator.__ifloordiv__(a, b)
	a = ifloordiv(a, b) is equivalent to a //= b.

operator.ilshift(a, b)
operator.__ilshift__(a, b)
	a = ilshift(a, b) is equivalent to a <<= b.

operator.imod(a, b)
operator.__imod__(a, b)
	a = imod(a, b) is equivalent to a %= b.

operator.imul(a, b)
operator.__imul__(a, b)
	a = imul(a, b) is equivalent to a *= b.

operator.imatmul(a, b)
operator.__imatmul__(a, b)
	a = imatmul(a, b) is equivalent to a @= b.

operator.ior(a, b)
operator.__ior__(a, b)
	a = ior(a, b) is equivalent to a |= b.

operator.ipow(a, b)
operator.__ipow__(a, b)
	a = ipow(a, b) is equivalent to a **= b.

operator.irshift(a, b)
operator.__irshift__(a, b)
	a = irshift(a, b) is equivalent to a >>= b.

operator.isub(a, b)
operator.__isub__(a, b)
	a = isub(a, b) is equivalent to a -= b.

operator.itruediv(a, b)
operator.__itruediv__(a, b)
	a = itruediv(a, b) is equivalent to a /= b.

operator.ixor(a, b)
operator.__ixor__(a, b)
	a = ixor(a, b) is equivalent to a ^= b.

数学运算

operator.abs(obj)
operator.__abs__(obj)
	Return the absolute value of obj.

operator.add(a, b)
operator.__add__(a, b)
	Return a + b, for a and b numbers.

operator.and_(a, b)
operator.__and__(a, b)
	Return the bitwise and of a and b.

operator.floordiv(a, b)
operator.__floordiv__(a, b)
	Return a // b.

operator.index(a)
operator.__index__(a)
	Return a converted to an integer. Equivalent to a.__index__().

operator.inv(obj)
operator.invert(obj)
operator.__inv__(obj)
operator.__invert__(obj)
	Return the bitwise inverse of the number obj. This is equivalent to ~obj.

operator.lshift(a, b)
operator.__lshift__(a, b)
	Return a shifted left by b.

operator.mod(a, b)
operator.__mod__(a, b)
	Return a % b.

operator.mul(a, b)
operator.__mul__(a, b)
	Return a * b, for a and b numbers.

operator.matmul(a, b)
operator.__matmul__(a, b)
	Return a @ b.

operator.neg(obj)
operator.__neg__(obj)
	Return obj negated (-obj).

operator.or_(a, b)
operator.__or__(a, b)
	Return the bitwise or of a and b.

operator.pos(obj)
operator.__pos__(obj)
Return obj positive (+obj).

operator.pow(a, b)
operator.__pow__(a, b)
	Return a ** b, for a and b numbers.

operator.rshift(a, b)
operator.__rshift__(a, b)
	Return a shifted right by b.

operator.sub(a, b)
operator.__sub__(a, b)
	Return a - b.

operator.truediv(a, b)
operator.__truediv__(a, b)
	Return a / b where 2/3 is .66 rather than 0. This is also known as "true" division.

operator.xor(a, b)
operator.__xor__(a, b)
	Return the bitwise exclusive or of a and b.

序列运算

operator.concat(a, b)
operator.__concat__(a, b)
	Return a + b for a and b sequences.

operator.contains(a, b)
operator.__contains__(a, b)
	Return the outcome of the test b in a. Note the reversed operands.

operator.countOf(a, b)
	Return the number of occurrences of b in a.

operator.delitem(a, b)
operator.__delitem__(a, b)
	Remove the value of a at index b.

operator.getitem(a, b)
operator.__getitem__(a, b)
	Return the value of a at index b.

operator.indexOf(a, b)
	Return the index of the first of occurrence of b in a.

operator.setitem(a, b, c)
operator.__setitem__(a, b, c)
	Set the value of a at index b to c.

operator.length_hint(obj, default=0)
	Return an estimated length for the object o. First try to return its actual length, then an estimate using object.__length_hint__(), and finally return the default value.

实用函数

operator.attrgetter

operator.attrgetter(attr)
operator.attrgetter(*attrs)

Return a callable object that fetches attr from its operand. If more than one attribute is requested, returns a tuple of attributes. The attribute names can also contain dots. For example:
	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).
	After f = attrgetter('name.first', 'name.last'), the call f(b) returns (b.name.first, b.name.last).

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_attr(obj, attr) for attr in items)
    return g

def resolve_attr(obj, attr):
    for name in attr.split("."):
        obj = getattr(obj, name)
    return obj

operator.itemgetter

operator.itemgetter(item)
operator.itemgetter(*items)

Return a callable object that fetches item from its operand using the operand’s __getitem__() method. If multiple items are specified, returns a tuple of lookup values. For example:
	After f = itemgetter(2), the call f(r) returns r[2].
	After g = itemgetter(2, 5, 3), the call g(r) returns (r[2], r[5], r[3]).

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 __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'

>>> soldier = dict(rank='captain', name='dotterbart')
>>> itemgetter('rank')(soldier)
'captain'

Example of using 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)]

operator.methodcaller

operator.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. For example:
	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

Mapping Operators to Functions

This table shows how abstract operations correspond to operator symbols in the Python syntax and the functions in the 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`
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)
Matrix Multiplication	a @ b	matmul(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)