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Diffstat (limited to 'Doc/library/collections.rst')
| -rw-r--r-- | Doc/library/collections.rst | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst index 8278ce4..1e32f99 100644 --- a/Doc/library/collections.rst +++ b/Doc/library/collections.rst @@ -58,7 +58,7 @@ ABC Inherits Abstract Methods Mixin M ``insert``, ``remove``, and ``__iadd__`` 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:`Container` ``__contains__`` ``__sub__``, ``__xor__``, and ``isdisjoint`` @@ -100,6 +100,23 @@ The ABC supplies the remaining methods such as :meth:`__and__` and s2 = ListBasedSet('defghi') 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`.) |