Backport doc readability improvements for the collections module.
This commit is contained in:
Raymond Hettinger
parent
a2156c0b36
commit
f56c9cd30d
|
|
@ -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`.
|
||||
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`.
|
||||
|
||||
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`.
|
||||
===================== ====================================================================
|
||||
: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 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`.
|
||||
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
|
||||
|
|
@ -1009,3 +902,117 @@ 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`.
|
||||
|
|
|
|||
Loading…
Reference in New Issue