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Document how to use Set and MutableSet as a mixin.

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This commit is contained in:
Raymond Hettinger 2008-02-09 03:25:08 +00:00
parent 74b6495b34
commit 7aebb64bab
2 changed files with 20 additions and 3 deletions
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19
Doc/library/collections.rst
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@ -58,7 +58,7 @@ ABC Inherits Abstract Methods Mixin M
``insert``, ``remove``, and ``__iadd__`` ``insert``, ``remove``, and ``__iadd__``
and ``__len__`` and ``__len__``
:class:`Set` :class:`Sized`, ``__len__``, ``__le__``, ``__lt__``, ``__eq__``, ``__ne__``, :class:`Set` \(1) \(2) :class:`Sized`, ``__len__``, ``__le__``, ``__lt__``, ``__eq__``, ``__ne__``,
:class:`Iterable`, ``__iter__``, and ``__gt__``, ``__ge__``, ``__and__``, ``__or__`` :class:`Iterable`, ``__iter__``, and ``__gt__``, ``__ge__``, ``__and__``, ``__or__``
:class:`Container` ``__contains__`` ``__sub__``, ``__xor__``, and ``isdisjoint`` :class:`Container` ``__contains__`` ``__sub__``, ``__xor__``, and ``isdisjoint``
@ -100,6 +100,23 @@ The ABC supplies the remaining methods such as :meth:`__and__` and
s2 = ListBasedSet('defghi') s2 = ListBasedSet('defghi')
overlap = s1 & s2 # The __and__() method is supported automatically overlap = s1 & s2 # The __and__() method is supported automatically
Notes on using :class:`Set` and :class:`MutableSet` as a mixin:
(1)
Since some set operations create new sets, the default mixin methods need
a way to create new instances from an iterable. The class constructor is
assumed to have a signature in the form ``ClassName(iterable)``.
That assumption is factored-out to a singleinternal classmethod called
:meth:`_from_iterable` which calls ``cls(iterable)`` to produce a new set.
If the :class:`Set` mixin is being used in a class with a different
constructor signature, you will need to override :meth:`from_iterable`
with a classmethod that can construct new instances from
an iterable argument.
(2)
To override the comparisons (presumably for speed, as the
semantics are fixed), redefine :meth:`__le__` and
then the other operations will automatically follow suit.
(For more about ABCs, see the :mod:`abc` module and :pep:`3119`.) (For more about ABCs, see the :mod:`abc` module and :pep:`3119`.)

4
Lib/_abcoll.py
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@ -207,9 +207,9 @@ class Set(Sized, Iterable, Container):
'''Construct an instance of the class from any iterable input. '''Construct an instance of the class from any iterable input.
Must override this method if the class constructor signature Must override this method if the class constructor signature
will not accept a frozenset for an input. does not accept an iterable for an input.
''' '''
return cls(frozenset(it)) return cls(it)
def __and__(self, other): def __and__(self, other):
if not isinstance(other, Iterable): if not isinstance(other, Iterable):