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# 9.9. `operator` — Standard operators as functions

The `operator` module exports a set of efficient functions 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:

`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)

  Perform 「rich comparisons」 between a and b. Specifically, `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 Comparisons for more information about rich comparisons.

  2.2 版新加入.

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 `__nonzero__()` 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.

  2.3 版新加入.

`operator.``is_not`(a, b)

  Return `a is not b`. Tests object identity.

  2.3 版新加入.

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.``div`(a, b)
`operator.``__div__`(a, b)

  Return `a / b` when `__future__.division` is not in effect. This is also known as 「classic」 division.

`operator.``floordiv`(a, b)
`operator.``__floordiv__`(a, b)

  Return `a // b`.

  2.2 版新加入.

`operator.``index`(a)
`operator.``__index__`(a)

  Return a converted to an integer. Equivalent to `a.__index__()`.

  2.5 版新加入.

`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`.

  2.0 版新加入: The names `invert()` and `__invert__()`.

`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.``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.

  2.3 版新加入.

`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` when `__future__.division` is in effect. This is also known as 「true」 division.

  2.2 版新加入.

`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.

  2.0 版新加入: The name `__contains__()`.

`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.``delslice`(a, b, c)
`operator.``__delslice__`(a, b, c)

  Delete the slice of a from index b to index c-1.

  2.6 版後已棄用: This function is removed in Python 3.x. Use `delitem()` with a slice index.

`operator.``getitem`(a, b)
`operator.``__getitem__`(a, b)

  Return the value of a at index b.

`operator.``getslice`(a, b, c)
`operator.``__getslice__`(a, b, c)

  Return the slice of a from index b to index c-1.

  2.6 版後已棄用: This function is removed in Python 3.x. Use `getitem()` with a slice index.

`operator.``indexOf`(a, b)

  Return the index of the first of occurrence of b in a.

`operator.``repeat`(a, b)
`operator.``__repeat__`(a, b)

  2.7 版後已棄用: Use `__mul__()` instead.

  Return `a * b` where a is a sequence and b is an integer.

`operator.``sequenceIncludes`(...)

  2.0 版後已棄用: Use `contains()` instead.

  Alias for `contains()`.

`operator.``setitem`(a, b, c)
`operator.``__setitem__`(a, b, c)

  Set the value of a at index b to c.

`operator.``setslice`(a, b, c, v)
`operator.``__setslice__`(a, b, c, v)

  Set the slice of a from index b to index c-1 to the sequence v.

  2.6 版後已棄用: This function is removed in Python 3.x. Use `setitem()` with a slice index.

Example use of operator functions:

    >>> # Elementwise multiplication
    >>> map(mul, [0, 1, 2, 3], [10, 20, 30, 40])
    [0, 20, 60, 120]

    >>> # Dot product
    >>> sum(map(mul, [0, 1, 2, 3], [10, 20, 30, 40]))
    200

Many operations have an 「in-place」 version. The following functions provide 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`.

`operator.``iadd`(a, b)
`operator.``__iadd__`(a, b)

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

  2.5 版新加入.

`operator.``iand`(a, b)
`operator.``__iand__`(a, b)

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

  2.5 版新加入.

`operator.``iconcat`(a, b)
`operator.``__iconcat__`(a, b)

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

  2.5 版新加入.

`operator.``idiv`(a, b)
`operator.``__idiv__`(a, b)

  `a = idiv(a, b)` is equivalent to `a /= b` when `__future__.division` is not in effect.

  2.5 版新加入.

`operator.``ifloordiv`(a, b)
`operator.``__ifloordiv__`(a, b)

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

  2.5 版新加入.

`operator.``ilshift`(a, b)
`operator.``__ilshift__`(a, b)

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

  2.5 版新加入.

`operator.``imod`(a, b)
`operator.``__imod__`(a, b)

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

  2.5 版新加入.

`operator.``imul`(a, b)
`operator.``__imul__`(a, b)

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

  2.5 版新加入.

`operator.``ior`(a, b)
`operator.``__ior__`(a, b)

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

  2.5 版新加入.

`operator.``ipow`(a, b)
`operator.``__ipow__`(a, b)

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

  2.5 版新加入.

`operator.``irepeat`(a, b)
`operator.``__irepeat__`(a, b)

  2.7 版後已棄用: Use `__imul__()` instead.

  `a = irepeat(a, b)` is equivalent to `a *= b` where a is a sequence and b is an integer.

  2.5 版新加入.

`operator.``irshift`(a, b)
`operator.``__irshift__`(a, b)

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

  2.5 版新加入.

`operator.``isub`(a, b)
`operator.``__isub__`(a, b)

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

  2.5 版新加入.

`operator.``itruediv`(a, b)
`operator.``__itruediv__`(a, b)

  `a = itruediv(a, b)` is equivalent to `a /= b` when `__future__.division` is in effect.

  2.5 版新加入.

`operator.``ixor`(a, b)
`operator.``__ixor__`(a, b)

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

  2.5 版新加入.

The `operator` module also defines a few predicates to test the type of objects; however, these are not all reliable. It is preferable to test abstract base classes instead (see `collections` and `numbers` for details).

`operator.``isCallable`(obj)

  2.0 版後已棄用: Use `isinstance(x, collections.Callable)` instead.

  Returns true if the object obj can be called like a function, otherwise it returns false. True is returned for functions, bound and unbound methods, class objects, and instance objects which support the `__call__()` method.

`operator.``isMappingType`(obj)

  2.7 版後已棄用: Use `isinstance(x, collections.Mapping)` instead.

  Returns true if the object obj supports the mapping interface. This is true for dictionaries and all instance objects defining `__getitem__()`.

`operator.``isNumberType`(obj)

  2.7 版後已棄用: Use `isinstance(x, numbers.Number)` instead.

  Returns true if the object obj represents a number. This is true for all numeric types implemented in C.

`operator.``isSequenceType`(obj)

  2.7 版後已棄用: Use `isinstance(x, collections.Sequence)` instead.

  Returns true if the object obj supports the sequence protocol. This returns true for all objects which define sequence methods in C, and for all instance objects defining `__getitem__()`.

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)`.

  Equivalent to:

      def attrgetter(*items):
          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

  2.4 版新加入.

  2.5 版更變: Added support for multiple attributes.

  2.6 版更變: Added support for dotted attributes.

`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'

  2.4 版新加入.

  2.5 版更變: Added support for multiple item extraction.

  Example of using `itemgetter()` to retrieve specific fields from a tuple record:

      >>> 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)]

`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

  2.6 版新加入.

## 9.9.1. 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.

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` | `div(a, b)` (without `__future__.division`)
Division | `a / b` | `truediv(a, b)` (with `__future__.division`)
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 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)`
Negation (Arithmetic) | `- a` | `neg(a)`
Negation (Logical) | `not a` | `not_(a)`
Positive | `+ a` | `pos(a)`
Right Shift | `a >> b` | `rshift(a, b)`
Sequence Repetition | `seq * i` | `repeat(seq, i)`
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)`