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-rw-r--r-- | Doc/library/collections.rst | 257 |
1 files changed, 132 insertions, 125 deletions
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst index 6c881f5..741c7a0 100644 --- a/Doc/library/collections.rst +++ b/Doc/library/collections.rst @@ -12,131 +12,24 @@ import itertools __name__ = '<doctest>' -This module implements high-performance container datatypes. Currently, -there are four datatypes, :class:`Counter`, :class:`deque`, :class:`OrderedDict` and -:class:`defaultdict`, and one datatype factory function, :func:`namedtuple`. - -The specialized containers provided in this module provide alternatives -to Python's general purpose built-in containers, :class:`dict`, -:class:`list`, :class:`set`, and :class:`tuple`. - -In addition to containers, the collections module provides some ABCs -(abstract base classes) that can be used to test whether a class -provides a particular interface, for example, whether it is hashable or -a mapping. - -ABCs - abstract base classes ----------------------------- - -The collections module offers the following ABCs: - -========================= ===================== ====================== ==================================================== -ABC Inherits Abstract Methods Mixin Methods -========================= ===================== ====================== ==================================================== -:class:`Container` ``__contains__`` -:class:`Hashable` ``__hash__`` -:class:`Iterable` ``__iter__`` -:class:`Iterator` :class:`Iterable` ``__next__`` ``__iter__`` -:class:`Sized` ``__len__`` -:class:`Callable` ``__call__`` - -:class:`Sequence` :class:`Sized`, ``__getitem__`` ``__contains__``. ``__iter__``, ``__reversed__``. - :class:`Iterable`, ``index``, and ``count`` - :class:`Container` - -:class:`MutableSequence` :class:`Sequence` ``__setitem__`` Inherited Sequence methods and - ``__delitem__``, ``append``, ``reverse``, ``extend``, ``pop``, - and ``insert`` ``remove``, and ``__iadd__`` - -:class:`Set` :class:`Sized`, ``__le__``, ``__lt__``, ``__eq__``, ``__ne__``, - :class:`Iterable`, ``__gt__``, ``__ge__``, ``__and__``, ``__or__`` - :class:`Container` ``__sub__``, ``__xor__``, and ``isdisjoint`` - -:class:`MutableSet` :class:`Set` ``add`` and Inherited Set methods and - ``discard`` ``clear``, ``pop``, ``remove``, ``__ior__``, - ``__iand__``, ``__ixor__``, and ``__isub__`` - -:class:`Mapping` :class:`Sized`, ``__getitem__`` ``__contains__``, ``keys``, ``items``, ``values``, - :class:`Iterable`, ``get``, ``__eq__``, and ``__ne__`` - :class:`Container` - -:class:`MutableMapping` :class:`Mapping` ``__setitem__`` and Inherited Mapping methods and - ``__delitem__`` ``pop``, ``popitem``, ``clear``, ``update``, - and ``setdefault`` - - -:class:`MappingView` :class:`Sized` ``__len__`` -:class:`KeysView` :class:`MappingView`, ``__contains__``, - :class:`Set` ``__iter__`` -:class:`ItemsView` :class:`MappingView`, ``__contains__``, - :class:`Set` ``__iter__`` -:class:`ValuesView` :class:`MappingView` ``__contains__``, ``__iter__`` -========================= ===================== ====================== ==================================================== - -These ABCs allow us to ask classes or instances if they provide -particular functionality, for example:: - - size = None - if isinstance(myvar, collections.Sized): - size = len(myvar) - -Several of the ABCs are also useful as mixins that make it easier to develop -classes supporting container APIs. For example, to write a class supporting -the full :class:`Set` API, it only necessary to supply the three underlying -abstract methods: :meth:`__contains__`, :meth:`__iter__`, and :meth:`__len__`. -The ABC supplies the remaining methods such as :meth:`__and__` and -:meth:`isdisjoint` :: - - class ListBasedSet(collections.Set): - ''' Alternate set implementation favoring space over speed - and not requiring the set elements to be hashable. ''' - def __init__(self, iterable): - self.elements = lst = [] - for value in iterable: - if value not in lst: - lst.append(value) - def __iter__(self): - return iter(self.elements) - def __contains__(self, value): - return value in self.elements - def __len__(self): - return len(self.elements) - - s1 = ListBasedSet('abcdef') - 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 an internal 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. - -(3) - The :class:`Set` mixin provides a :meth:`_hash` method to compute a hash value - for the set; however, :meth:`__hash__` is not defined because not all sets - are hashable or immutable. To add set hashabilty using mixins, - inherit from both :meth:`Set` and :meth:`Hashable`, then define - ``__hash__ = Set._hash``. - -.. seealso:: - - * `OrderedSet recipe <http://code.activestate.com/recipes/576694/>`_ for an - example built on :class:`MutableSet`. - - * For more about ABCs, see the :mod:`abc` module and :pep:`3119`. +This module implements specialized container datatypes providing alternatives to +Python's general purpose built-in containers, :class:`dict`, :class:`list`, +:class:`set`, and :class:`tuple`. + +===================== ==================================================================== +:func:`namedtuple` factory function for creating tuple subclasses with named fields +:class:`deque` list-like container with fast appends and pops on either end +:class:`Counter` dict subclass for counting hashable objects +:class:`OrderedDict` dict subclass that remembers the order entries were added +:class:`defaultdict` dict subclass that calls a factory function to supply missing values +:class:`UserDict` wrapper around dictionary objects for easier dict subclassing +:class:`UserList` wrapper around list objects for easier list subclassing +:class:`UserString` wrapper around string objects for easier string subclassing +===================== ==================================================================== + +In addition to the concrete container classes, the collections module provides +ABCs (abstract base classes) that can be used to test whether a class provides a +particular interface, for example, whether it is hashable or a mapping. :class:`Counter` objects @@ -1036,3 +929,117 @@ attribute. be an instance of :class:`bytes`, :class:`str`, :class:`UserString` (or a subclass) or an arbitrary sequence which can be converted into a string using the built-in :func:`str` function. + + +ABCs - abstract base classes +---------------------------- + +The collections module offers the following ABCs: + +========================= ===================== ====================== ==================================================== +ABC Inherits Abstract Methods Mixin Methods +========================= ===================== ====================== ==================================================== +:class:`Container` ``__contains__`` +:class:`Hashable` ``__hash__`` +:class:`Iterable` ``__iter__`` +:class:`Iterator` :class:`Iterable` ``__next__`` ``__iter__`` +:class:`Sized` ``__len__`` +:class:`Callable` ``__call__`` + +:class:`Sequence` :class:`Sized`, ``__getitem__`` ``__contains__``. ``__iter__``, ``__reversed__``. + :class:`Iterable`, ``index``, and ``count`` + :class:`Container` + +:class:`MutableSequence` :class:`Sequence` ``__setitem__`` Inherited Sequence methods and + ``__delitem__``, ``append``, ``reverse``, ``extend``, ``pop``, + and ``insert`` ``remove``, and ``__iadd__`` + +:class:`Set` :class:`Sized`, ``__le__``, ``__lt__``, ``__eq__``, ``__ne__``, + :class:`Iterable`, ``__gt__``, ``__ge__``, ``__and__``, ``__or__`` + :class:`Container` ``__sub__``, ``__xor__``, and ``isdisjoint`` + +:class:`MutableSet` :class:`Set` ``add`` and Inherited Set methods and + ``discard`` ``clear``, ``pop``, ``remove``, ``__ior__``, + ``__iand__``, ``__ixor__``, and ``__isub__`` + +:class:`Mapping` :class:`Sized`, ``__getitem__`` ``__contains__``, ``keys``, ``items``, ``values``, + :class:`Iterable`, ``get``, ``__eq__``, and ``__ne__`` + :class:`Container` + +:class:`MutableMapping` :class:`Mapping` ``__setitem__`` and Inherited Mapping methods and + ``__delitem__`` ``pop``, ``popitem``, ``clear``, ``update``, + and ``setdefault`` + + +:class:`MappingView` :class:`Sized` ``__len__`` +:class:`KeysView` :class:`MappingView`, ``__contains__``, + :class:`Set` ``__iter__`` +:class:`ItemsView` :class:`MappingView`, ``__contains__``, + :class:`Set` ``__iter__`` +:class:`ValuesView` :class:`MappingView` ``__contains__``, ``__iter__`` +========================= ===================== ====================== ==================================================== + +These ABCs allow us to ask classes or instances if they provide +particular functionality, for example:: + + size = None + if isinstance(myvar, collections.Sized): + size = len(myvar) + +Several of the ABCs are also useful as mixins that make it easier to develop +classes supporting container APIs. For example, to write a class supporting +the full :class:`Set` API, it only necessary to supply the three underlying +abstract methods: :meth:`__contains__`, :meth:`__iter__`, and :meth:`__len__`. +The ABC supplies the remaining methods such as :meth:`__and__` and +:meth:`isdisjoint` :: + + class ListBasedSet(collections.Set): + ''' Alternate set implementation favoring space over speed + and not requiring the set elements to be hashable. ''' + def __init__(self, iterable): + self.elements = lst = [] + for value in iterable: + if value not in lst: + lst.append(value) + def __iter__(self): + return iter(self.elements) + def __contains__(self, value): + return value in self.elements + def __len__(self): + return len(self.elements) + + s1 = ListBasedSet('abcdef') + 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 an internal 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. + +(3) + The :class:`Set` mixin provides a :meth:`_hash` method to compute a hash value + for the set; however, :meth:`__hash__` is not defined because not all sets + are hashable or immutable. To add set hashabilty using mixins, + inherit from both :meth:`Set` and :meth:`Hashable`, then define + ``__hash__ = Set._hash``. + +.. seealso:: + + * `OrderedSet recipe <http://code.activestate.com/recipes/576694/>`_ for an + example built on :class:`MutableSet`. + + * For more about ABCs, see the :mod:`abc` module and :pep:`3119`. |