operator —- 标准运算符替代函数

源代码:Lib/operator.py

operator 模块提供了一套与Python的内置运算符对应的高效率函数。例如，operator.add(x, y) 与表达式 x+y 相同。 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。

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)
• 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)
• 在 a 和 b 之间进行全比较。具体的，lt(a, b) 与 a < b 相同， le(a, b) 与 a <= b 相同，eq(a, b) 与 a == b 相同，ne(a, b) 与 a != b 相同，gt(a, b) 与 a > b 相同，ge(a, b)与a >= b 相同。注意这些函数可以返回任何值，无论它是否可当作布尔值。关于全比较的更多信息请参考 比较运算 。

The logical operations are also generally applicable to all objects, and supporttruth tests, identity tests, and boolean operations:

• operator.not(_obj)
• operator.not(obj)

• Return the outcome of notobj. (Note that there is nonot() method for object instances; only the interpreter core definesthis operation. The result is affected by the bool() andlen() methods.)

• operator.truth(obj)

• Return True if obj is true, and False otherwise. This isequivalent to using the bool constructor.

• operator.is(_a, b)

• 返回 a is b. 测试对象标识。

• operator.isnot(_a, b)

• 返回 a is not b. 测试对象标识。

The mathematical and bitwise operations are the most numerous:

• operator.abs(obj)
• operator.abs(obj)

• 返回 obj 的绝对值。

• operator.add(a, b)

• operator.add(a, b)

• Return a + b, for a and b numbers.

• operator.and(_a, b)

• operator.and(a, b)

• 返回 x 和 y 按位与

• operator.floordiv(a, b)

• operator.floordiv(a, b)

• 返回 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)

• 返回 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)
• 返回 a @ b.

3.5 新版功能.

• 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)

• 返回 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.

Operations which work with sequences (some of them with mappings too) include:

• 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)

• 返回 b 在 a 中的出现次数。

• 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.lengthhint(_obj, default=0)

• Return an estimated length for the object o. First try to return itsactual length, then an estimate using object.length_hint(), andfinally return the default value.

3.4 新版功能.

The operator module also defines tools for generalized attribute and itemlookups. These are useful for making fast field extractors as arguments formap(), sorted(), itertools.groupby(), or other functions thatexpect a function argument.

• 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).

等价于:

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(item)
• operator.itemgetter(*items)

• Return a callable object that fetches item from its operand using theoperand'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]).

等价于:

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, andstrings accept an index or a slice:

>>> itemgetter('name')({'name': 'tu', 'age': 18})
'tu'
>>> 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 atuple 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(name, /, *args, **kwargs)

• Return a callable object that calls the method name on its operand. Ifadditional arguments and/or keyword arguments are given, they will be givento 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).

等价于:

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 thePython syntax and the functions in the operator module.

In-place Operators

Many operations have an "in-place" version. Listed below are functionsproviding a more primitive access to in-place operators than the usual syntaxdoes; for example, the statement x += y is equivalent tox = operator.iadd(x, y). Another way to put it is to say thatz = operator.iadd(x, y) is equivalent to the compound statementz = x; z += y.

In those examples, note that when an in-place method is called, the computationand assignment are performed in two separate steps. The in-place functionslisted below only do the first step, calling the in-place method. The secondstep, assignment, is not handled.

For immutable targets such as strings, numbers, and tuples, the updatedvalue 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 in-place methodwill 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.

3.5 新版功能.

• 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.