# 10.3. `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 support truth tests, identity tests, and boolean operations:

`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.

The mathematical and bitwise operations are the most numerous:

`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`.

  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)

  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.

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)

  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.

  3.4 新版功能.

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.

`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 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])`.

  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, 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 `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`(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)`.

  等价于:

      def methodcaller(name, *args, **kwargs):
          def caller(obj):
              return getattr(obj, name)(*args, **kwargs)
          return caller

## 10.3.1. 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.

运算 | 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 是 b` | `is_(a, b)`
Identity | `a 不是 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)`

## 10.3.2. 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 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`.

  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`.