
``operator`` --- Standard operators as functions
************************************************

The ``operator`` module exports a set of functions implemented in C
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.

   New in version 2.2.

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.

   New in version 2.3.

operator.is_not(a, b)

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

   New in version 2.3.

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``.

   New in version 2.2.

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``.

   New in version 2.0: 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.

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.

operator.pow(a, b)
operator.__pow__(a, b)

   Return ``a ** b``, for *a* and *b* numbers.

   New in version 2.3.

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.

   New in version 2.2.

operator.xor(a, b)
operator.__xor__(a, b)

   Return the bitwise exclusive or of *a* and *b*.

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

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

   New in version 2.5.

Operations which work with sequences 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.

   New in version 2.0: 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*.

   Deprecated since version 2.6: 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*.

   Deprecated since version 2.6: 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)

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

operator.sequenceIncludes(...)

   Deprecated since version 2.0: 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*.

   Deprecated since version 2.6: This function is removed in Python
   3.x.  Use ``setitem()`` with a slice index.

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``.

   New in version 2.5.

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

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

   New in version 2.5.

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

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

   New in version 2.5.

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

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

   New in version 2.5.

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

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

   New in version 2.5.

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

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

   New in version 2.5.

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

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

   New in version 2.5.

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

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

   New in version 2.5.

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

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

   New in version 2.5.

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

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

   New in version 2.5.

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

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

   New in version 2.5.

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

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

   New in version 2.5.

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

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

   New in version 2.5.

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

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

   New in version 2.5.

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

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

   New in version 2.5.

The ``operator`` module also defines a few predicates to test the type
of objects.

Note: Be careful not to misinterpret the results of these functions; only
  ``isCallable()`` has any measure of reliability with instance
  objects. For example:

  >>> class C:
  ...     pass
  ...
  >>> import operator
  >>> obj = C()
  >>> operator.isMappingType(obj)
  True

Note: Python 3 is expected to introduce abstract base classes for
  collection types, so it should be possible to write, for example,
  ``isinstance(obj, collections.Mapping)`` and ``isinstance(obj,
  collections.Sequence)``.

operator.isCallable(obj)

   Deprecated since version 2.0: Use the ``callable()`` built-in
   function 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)

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

   Warning: There is no reliable way to test if an instance supports the
     complete mapping protocol since the interface itself is ill-
     defined.  This makes this test less useful than it otherwise
     might be.

operator.isNumberType(obj)

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

   Warning: There is no reliable way to test if an instance supports the
     complete numeric interface since the interface itself is ill-
     defined.  This makes this test less useful than it otherwise
     might be.

operator.isSequenceType(obj)

   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__()``.

   Warning: There is no reliable way to test if an instance supports the
     complete sequence interface since the interface itself is ill-
     defined.  This makes this test less useful than it otherwise
     might be.

Example: Build a dictionary that maps the ordinals from ``0`` to
``255`` to their character equivalents.

>>> d = {}
>>> keys = range(256)
>>> vals = map(chr, keys)
>>> map(operator.setitem, [d]*len(keys), keys, vals)   # doctest: +SKIP

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[, args...])

   Return a callable object that fetches *attr* from its operand. If
   more than one attribute is requested, returns a tuple of
   attributes. 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)``.

   The attribute names can also contain dots; after ``f =
   attrgetter('date.month')``, the call ``f(b)`` returns
   ``b.date.month``.

   New in version 2.4.

   Changed in version 2.5: Added support for multiple attributes.

   Changed in version 2.6: Added support for dotted attributes.

operator.itemgetter(item[, args...])

   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.  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'

   New in version 2.4.

   Changed in version 2.5: 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.  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)``.

   New in version 2.6.


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)``                       |
+-------------------------+---------------------------+-----------------------------------+
| Right Shift             | ``a >> b``                | ``rshift(a, b)``                  |
+-------------------------+---------------------------+-----------------------------------+
| Sequence Repetition     | ``seq * i``               | ``repeat(seq, i)``                |
+-------------------------+---------------------------+-----------------------------------+
| Slice Assignment        | ``seq[i:j] = values``     | ``setslice(seq, i, j, values)``   |
+-------------------------+---------------------------+-----------------------------------+
| Slice Deletion          | ``del seq[i:j]``          | ``delslice(seq, i, j)``           |
+-------------------------+---------------------------+-----------------------------------+
| Slicing                 | ``seq[i:j]``              | ``getslice(seq, 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)``                      |
+-------------------------+---------------------------+-----------------------------------+
