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扩展阅读：

• operator — Standard operators as functions
• operator — 内置操作符接口

operator - Standard operators as functions

operater 模块导出了一组与 Python 的内部运算符相对应的函数。例如 operator.add(x, y) 等价于表达式 x+y。

在本模块中，大多数函数名直接使用对应的特殊方法名(但不带下划线)。为了向后兼容，本模块中的许多方法还保留了具备双下划线方法名的变体。为了使代码易读，请优先使用没有双下划线的版本。

本模块中的方法可分为以下四类：

• 对象比较(object comparisons)
• 逻辑运算(logical operations)
• 数学运算(mathematical operations)和位运算(bitwise operations)
• 序列操作(sequence operations)

运算符和函数的映射关系

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.

对象比较

支持所有的富比较运算符，并以对应的丰富比较运算符来命名：

operator.lt(a, b)
operator.le(a, b)
operator.eq(a, b)
operator.ne(a, b)
operator.ge(a, b)
operator.gt(a, b)
operator.__lt__(a, b)
operator.__le__(a, b)
operator.__eq__(a, b)
operator.__ne__(a, b)
operator.__ge__(a, b)
operator.__gt__(a, b)

具体来说，当在 a 和 b 之间执行"富比较"时：

• 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
• ge(a, b) is equivalent to a >=b.

注意：以上方法可以返回任意值，这些值可能会(也可能不会)被解释为布尔值。有关丰富比较的详细信息，请参阅 Comparisons 。

逻辑运算

逻辑操作通常也适用于所有对象，并支持真值测试，身份(identity)测试和布尔操作：

operator.not_(obj)
operator.__not__(obj)
# Return the outcome of not obj. (Note that there is no __not__() method for object instances; only the interpreter core defines this operation. The result is affected by the __bool__() and __len__() methods.)

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.

数学运算和位运算

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.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.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.
# New in version 3.5.

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

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.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.

位运算

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

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

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

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

序列操作

以下操作工作于序列(部分也可用于映射)之上：

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.
# New in version 3.4.

属性和项获取器

operator 模块还定义了用于通用属性和项查找的工具。这些工具可用于 map(), sorted(), itertools.groupby() 等函数的键函数，以便快速提取相应的字段。

获取器(getter)的开销比 lambda (或普通函数)小。

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

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)]

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

Inplace Operators

大多数运算符都有 “in-place” 版本。下面列出的函数提供了比常用语法更原始的访问方法。例如：

• 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.

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']

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.
# New in version 3.5.

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.