author | Shane McErlean <shane.mcerlean@accenture.com> |
Fri, 27 Aug 2010 15:33:49 +0100 | |
changeset 101 | 1e82a8be084a |
parent 1 | 2fb8b9db1c86 |
permissions | -rw-r--r-- |
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:mod:`collections` --- High-performance container datatypes |
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=========================================================== |
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.. module:: collections |
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:synopsis: High-performance datatypes |
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.. moduleauthor:: Raymond Hettinger <python@rcn.com> |
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.. sectionauthor:: Raymond Hettinger <python@rcn.com> |
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.. versionadded:: 2.4 |
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.. testsetup:: * |
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from collections import * |
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import itertools |
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__name__ = '<doctest>' |
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This module implements high-performance container datatypes. Currently, |
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there are two datatypes, :class:`deque` and :class:`defaultdict`, and |
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one datatype factory function, :func:`namedtuple`. |
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.. versionchanged:: 2.5 |
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Added :class:`defaultdict`. |
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.. versionchanged:: 2.6 |
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Added :func:`namedtuple`. |
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The specialized containers provided in this module provide alternatives |
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to Python's general purpose built-in containers, :class:`dict`, |
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:class:`list`, :class:`set`, and :class:`tuple`. |
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Besides the containers provided here, the optional :mod:`bsddb` |
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module offers the ability to create in-memory or file based ordered |
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dictionaries with string keys using the :meth:`bsddb.btopen` method. |
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In addition to containers, the collections module provides some ABCs |
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(abstract base classes) that can be used to test whether a class |
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provides a particular interface, for example, is it hashable or |
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a mapping. |
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.. versionchanged:: 2.6 |
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Added abstract base classes. |
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ABCs - abstract base classes |
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---------------------------- |
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The collections module offers the following ABCs: |
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========================= ===================== ====================== ==================================================== |
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ABC Inherits Abstract Methods Mixin Methods |
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========================= ===================== ====================== ==================================================== |
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:class:`Container` ``__contains__`` |
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:class:`Hashable` ``__hash__`` |
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:class:`Iterable` ``__iter__`` |
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:class:`Iterator` :class:`Iterable` ``__next__`` ``__iter__`` |
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:class:`Sized` ``__len__`` |
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:class:`Callable` ``__call__`` |
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:class:`Sequence` :class:`Sized`, ``__getitem__`` ``__contains__``. ``__iter__``, ``__reversed__``. |
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:class:`Iterable`, and ``__len__`` ``index``, and ``count`` |
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:class:`Container` |
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:class:`MutableSequnce` :class:`Sequence` ``__getitem__`` Inherited Sequence methods and |
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``__delitem__``, ``append``, ``reverse``, ``extend``, ``pop``, |
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``insert``, ``remove``, and ``__iadd__`` |
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and ``__len__`` |
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:class:`Set` :class:`Sized`, ``__len__``, ``__le__``, ``__lt__``, ``__eq__``, ``__ne__``, |
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:class:`Iterable`, ``__iter__``, and ``__gt__``, ``__ge__``, ``__and__``, ``__or__`` |
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:class:`Container` ``__contains__`` ``__sub__``, ``__xor__``, and ``isdisjoint`` |
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:class:`MutableSet` :class:`Set` ``add`` and Inherited Set methods and |
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``discard`` ``clear``, ``pop``, ``remove``, ``__ior__``, |
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``__iand__``, ``__ixor__``, and ``__isub__`` |
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:class:`Mapping` :class:`Sized`, ``__getitem__``, ``__contains__``, ``keys``, ``items``, ``values``, |
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:class:`Iterable`, ``__len__``. and ``get``, ``__eq__``, and ``__ne__`` |
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:class:`Container` ``__iter__`` |
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:class:`MutableMapping` :class:`Mapping` ``__getitem__`` Inherited Mapping methods and |
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``__setitem__``, ``pop``, ``popitem``, ``clear``, ``update``, |
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``__delitem__``, and ``setdefault`` |
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``__iter__``, and |
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``__len__`` |
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:class:`MappingView` :class:`Sized` ``__len__`` |
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:class:`KeysView` :class:`MappingView`, ``__contains__``, |
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:class:`Set` ``__iter__`` |
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:class:`ItemsView` :class:`MappingView`, ``__contains__``, |
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:class:`Set` ``__iter__`` |
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:class:`ValuesView` :class:`MappingView` ``__contains__``, ``__iter__`` |
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========================= ===================== ====================== ==================================================== |
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These ABCs allow us to ask classes or instances if they provide |
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particular functionality, for example:: |
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size = None |
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if isinstance(myvar, collections.Sized): |
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size = len(myvar) |
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Several of the ABCs are also useful as mixins that make it easier to develop |
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classes supporting container APIs. For example, to write a class supporting |
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the full :class:`Set` API, it only necessary to supply the three underlying |
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abstract methods: :meth:`__contains__`, :meth:`__iter__`, and :meth:`__len__`. |
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|
105 |
The ABC supplies the remaining methods such as :meth:`__and__` and |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
106 |
:meth:`isdisjoint` :: |
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|
107 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
108 |
class ListBasedSet(collections.Set): |
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|
109 |
''' Alternate set implementation favoring space over speed |
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|
110 |
and not requiring the set elements to be hashable. ''' |
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|
111 |
def __init__(self, iterable): |
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|
112 |
self.elements = lst = [] |
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|
113 |
for value in iterable: |
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|
114 |
if value not in lst: |
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|
115 |
lst.append(value) |
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|
116 |
def __iter__(self): |
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117 |
return iter(self.elements) |
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|
118 |
def __contains__(self, value): |
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119 |
return value in self.elements |
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|
120 |
def __len__(self): |
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121 |
return len(self.elements) |
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|
122 |
|
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|
123 |
s1 = ListBasedSet('abcdef') |
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124 |
s2 = ListBasedSet('defghi') |
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|
125 |
overlap = s1 & s2 # The __and__() method is supported automatically |
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|
126 |
|
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|
127 |
Notes on using :class:`Set` and :class:`MutableSet` as a mixin: |
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|
128 |
|
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|
129 |
(1) |
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|
130 |
Since some set operations create new sets, the default mixin methods need |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
131 |
a way to create new instances from an iterable. The class constructor is |
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|
132 |
assumed to have a signature in the form ``ClassName(iterable)``. |
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|
133 |
That assumption is factored-out to an internal classmethod called |
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|
134 |
:meth:`_from_iterable` which calls ``cls(iterable)`` to produce a new set. |
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|
135 |
If the :class:`Set` mixin is being used in a class with a different |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
136 |
constructor signature, you will need to override :meth:`from_iterable` |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
137 |
with a classmethod that can construct new instances from |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
138 |
an iterable argument. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
139 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
140 |
(2) |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
141 |
To override the comparisons (presumably for speed, as the |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
142 |
semantics are fixed), redefine :meth:`__le__` and |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
143 |
then the other operations will automatically follow suit. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
144 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
145 |
(3) |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
146 |
The :class:`Set` mixin provides a :meth:`_hash` method to compute a hash value |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
147 |
for the set; however, :meth:`__hash__` is not defined because not all sets |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
148 |
are hashable or immutable. To add set hashabilty using mixins, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
149 |
inherit from both :meth:`Set` and :meth:`Hashable`, then define |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
150 |
``__hash__ = Set._hash``. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
151 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
152 |
(For more about ABCs, see the :mod:`abc` module and :pep:`3119`.) |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
153 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
154 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
155 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
156 |
.. _deque-objects: |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
157 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
158 |
:class:`deque` objects |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
159 |
---------------------- |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
160 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
161 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
162 |
.. class:: deque([iterable[, maxlen]]) |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
163 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
164 |
Returns a new deque object initialized left-to-right (using :meth:`append`) with |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
165 |
data from *iterable*. If *iterable* is not specified, the new deque is empty. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
166 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
167 |
Deques are a generalization of stacks and queues (the name is pronounced "deck" |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
168 |
and is short for "double-ended queue"). Deques support thread-safe, memory |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
169 |
efficient appends and pops from either side of the deque with approximately the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
170 |
same O(1) performance in either direction. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
171 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
172 |
Though :class:`list` objects support similar operations, they are optimized for |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
173 |
fast fixed-length operations and incur O(n) memory movement costs for |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
174 |
``pop(0)`` and ``insert(0, v)`` operations which change both the size and |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
175 |
position of the underlying data representation. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
176 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
177 |
.. versionadded:: 2.4 |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
178 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
179 |
If *maxlen* is not specified or is *None*, deques may grow to an |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
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|
180 |
arbitrary length. Otherwise, the deque is bounded to the specified maximum |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
181 |
length. Once a bounded length deque is full, when new items are added, a |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
182 |
corresponding number of items are discarded from the opposite end. Bounded |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
183 |
length deques provide functionality similar to the ``tail`` filter in |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
184 |
Unix. They are also useful for tracking transactions and other pools of data |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
185 |
where only the most recent activity is of interest. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
186 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
187 |
.. versionchanged:: 2.6 |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
188 |
Added *maxlen* parameter. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
189 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
190 |
Deque objects support the following methods: |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
191 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
192 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
193 |
.. method:: append(x) |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
194 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
195 |
Add *x* to the right side of the deque. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
196 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
197 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
198 |
.. method:: appendleft(x) |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
199 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
200 |
Add *x* to the left side of the deque. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
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|
201 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
202 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
203 |
.. method:: clear() |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
204 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
205 |
Remove all elements from the deque leaving it with length 0. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
206 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
207 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
208 |
.. method:: extend(iterable) |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
209 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
210 |
Extend the right side of the deque by appending elements from the iterable |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
211 |
argument. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
212 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
213 |
|
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.. method:: extendleft(iterable) |
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Extend the left side of the deque by appending elements from *iterable*. |
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Note, the series of left appends results in reversing the order of |
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elements in the iterable argument. |
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.. method:: pop() |
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Remove and return an element from the right side of the deque. If no |
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elements are present, raises an :exc:`IndexError`. |
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.. method:: popleft() |
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Remove and return an element from the left side of the deque. If no |
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elements are present, raises an :exc:`IndexError`. |
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.. method:: remove(value) |
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Removed the first occurrence of *value*. If not found, raises a |
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:exc:`ValueError`. |
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237 |
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.. versionadded:: 2.5 |
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.. method:: rotate(n) |
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Rotate the deque *n* steps to the right. If *n* is negative, rotate to |
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the left. Rotating one step to the right is equivalent to: |
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``d.appendleft(d.pop())``. |
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In addition to the above, deques support iteration, pickling, ``len(d)``, |
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``reversed(d)``, ``copy.copy(d)``, ``copy.deepcopy(d)``, membership testing with |
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the :keyword:`in` operator, and subscript references such as ``d[-1]``. Indexed |
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access is O(1) at both ends but slows to O(n) in the middle. For fast random |
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access, use lists instead. |
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Example: |
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|
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.. doctest:: |
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|
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>>> from collections import deque |
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>>> d = deque('ghi') # make a new deque with three items |
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>>> for elem in d: # iterate over the deque's elements |
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... print elem.upper() |
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G |
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H |
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I |
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|
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>>> d.append('j') # add a new entry to the right side |
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>>> d.appendleft('f') # add a new entry to the left side |
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>>> d # show the representation of the deque |
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deque(['f', 'g', 'h', 'i', 'j']) |
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|
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>>> d.pop() # return and remove the rightmost item |
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'j' |
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>>> d.popleft() # return and remove the leftmost item |
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'f' |
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>>> list(d) # list the contents of the deque |
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['g', 'h', 'i'] |
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>>> d[0] # peek at leftmost item |
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'g' |
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>>> d[-1] # peek at rightmost item |
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'i' |
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|
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>>> list(reversed(d)) # list the contents of a deque in reverse |
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['i', 'h', 'g'] |
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>>> 'h' in d # search the deque |
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True |
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>>> d.extend('jkl') # add multiple elements at once |
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>>> d |
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deque(['g', 'h', 'i', 'j', 'k', 'l']) |
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>>> d.rotate(1) # right rotation |
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>>> d |
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deque(['l', 'g', 'h', 'i', 'j', 'k']) |
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>>> d.rotate(-1) # left rotation |
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>>> d |
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deque(['g', 'h', 'i', 'j', 'k', 'l']) |
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|
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>>> deque(reversed(d)) # make a new deque in reverse order |
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deque(['l', 'k', 'j', 'i', 'h', 'g']) |
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>>> d.clear() # empty the deque |
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>>> d.pop() # cannot pop from an empty deque |
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Traceback (most recent call last): |
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File "<pyshell#6>", line 1, in -toplevel- |
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d.pop() |
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IndexError: pop from an empty deque |
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|
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>>> d.extendleft('abc') # extendleft() reverses the input order |
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>>> d |
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deque(['c', 'b', 'a']) |
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|
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|
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.. _deque-recipes: |
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|
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:class:`deque` Recipes |
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^^^^^^^^^^^^^^^^^^^^^^ |
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|
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This section shows various approaches to working with deques. |
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316 |
|
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The :meth:`rotate` method provides a way to implement :class:`deque` slicing and |
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deletion. For example, a pure python implementation of ``del d[n]`` relies on |
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|
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the :meth:`rotate` method to position elements to be popped:: |
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320 |
|
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def delete_nth(d, n): |
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322 |
d.rotate(-n) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
323 |
d.popleft() |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
324 |
d.rotate(n) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
325 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
326 |
To implement :class:`deque` slicing, use a similar approach applying |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
327 |
:meth:`rotate` to bring a target element to the left side of the deque. Remove |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
328 |
old entries with :meth:`popleft`, add new entries with :meth:`extend`, and then |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
329 |
reverse the rotation. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
330 |
With minor variations on that approach, it is easy to implement Forth style |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
331 |
stack manipulations such as ``dup``, ``drop``, ``swap``, ``over``, ``pick``, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
332 |
``rot``, and ``roll``. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
333 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
334 |
Multi-pass data reduction algorithms can be succinctly expressed and efficiently |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
335 |
coded by extracting elements with multiple calls to :meth:`popleft`, applying |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
336 |
a reduction function, and calling :meth:`append` to add the result back to the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
337 |
deque. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
338 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
339 |
For example, building a balanced binary tree of nested lists entails reducing |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
340 |
two adjacent nodes into one by grouping them in a list: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
341 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
342 |
>>> def maketree(iterable): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
343 |
... d = deque(iterable) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
344 |
... while len(d) > 1: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
345 |
... pair = [d.popleft(), d.popleft()] |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
346 |
... d.append(pair) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
347 |
... return list(d) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
348 |
... |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
349 |
>>> print maketree('abcdefgh') |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
350 |
[[[['a', 'b'], ['c', 'd']], [['e', 'f'], ['g', 'h']]]] |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
351 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
352 |
Bounded length deques provide functionality similar to the ``tail`` filter |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
353 |
in Unix:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
354 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
355 |
def tail(filename, n=10): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
356 |
'Return the last n lines of a file' |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
357 |
return deque(open(filename), n) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
358 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
359 |
.. _defaultdict-objects: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
360 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
361 |
:class:`defaultdict` objects |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
362 |
---------------------------- |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
363 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
364 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
365 |
.. class:: defaultdict([default_factory[, ...]]) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
366 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
367 |
Returns a new dictionary-like object. :class:`defaultdict` is a subclass of the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
368 |
builtin :class:`dict` class. It overrides one method and adds one writable |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
369 |
instance variable. The remaining functionality is the same as for the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
370 |
:class:`dict` class and is not documented here. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
371 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
372 |
The first argument provides the initial value for the :attr:`default_factory` |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
373 |
attribute; it defaults to ``None``. All remaining arguments are treated the same |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
374 |
as if they were passed to the :class:`dict` constructor, including keyword |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
375 |
arguments. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
376 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
377 |
.. versionadded:: 2.5 |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
378 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
379 |
:class:`defaultdict` objects support the following method in addition to the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
380 |
standard :class:`dict` operations: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
381 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
382 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
383 |
.. method:: defaultdict.__missing__(key) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
384 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
385 |
If the :attr:`default_factory` attribute is ``None``, this raises a |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
386 |
:exc:`KeyError` exception with the *key* as argument. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
387 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
388 |
If :attr:`default_factory` is not ``None``, it is called without arguments |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
389 |
to provide a default value for the given *key*, this value is inserted in |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
390 |
the dictionary for the *key*, and returned. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
391 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
392 |
If calling :attr:`default_factory` raises an exception this exception is |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
393 |
propagated unchanged. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
394 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
395 |
This method is called by the :meth:`__getitem__` method of the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
396 |
:class:`dict` class when the requested key is not found; whatever it |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
397 |
returns or raises is then returned or raised by :meth:`__getitem__`. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
398 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
399 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
400 |
:class:`defaultdict` objects support the following instance variable: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
401 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
402 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
403 |
.. attribute:: defaultdict.default_factory |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
404 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
405 |
This attribute is used by the :meth:`__missing__` method; it is |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
406 |
initialized from the first argument to the constructor, if present, or to |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
407 |
``None``, if absent. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
408 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
409 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
410 |
.. _defaultdict-examples: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
411 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
412 |
:class:`defaultdict` Examples |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
413 |
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
414 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
415 |
Using :class:`list` as the :attr:`default_factory`, it is easy to group a |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
416 |
sequence of key-value pairs into a dictionary of lists: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
417 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
418 |
>>> s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)] |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
419 |
>>> d = defaultdict(list) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
420 |
>>> for k, v in s: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
421 |
... d[k].append(v) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
422 |
... |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
423 |
>>> d.items() |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
424 |
[('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])] |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
425 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
426 |
When each key is encountered for the first time, it is not already in the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
427 |
mapping; so an entry is automatically created using the :attr:`default_factory` |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
428 |
function which returns an empty :class:`list`. The :meth:`list.append` |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
429 |
operation then attaches the value to the new list. When keys are encountered |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
430 |
again, the look-up proceeds normally (returning the list for that key) and the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
431 |
:meth:`list.append` operation adds another value to the list. This technique is |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
432 |
simpler and faster than an equivalent technique using :meth:`dict.setdefault`: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
433 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
434 |
>>> d = {} |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
435 |
>>> for k, v in s: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
436 |
... d.setdefault(k, []).append(v) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
437 |
... |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
438 |
>>> d.items() |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
439 |
[('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])] |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
440 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
441 |
Setting the :attr:`default_factory` to :class:`int` makes the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
442 |
:class:`defaultdict` useful for counting (like a bag or multiset in other |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
443 |
languages): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
444 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
445 |
>>> s = 'mississippi' |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
446 |
>>> d = defaultdict(int) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
447 |
>>> for k in s: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
448 |
... d[k] += 1 |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
449 |
... |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
450 |
>>> d.items() |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
451 |
[('i', 4), ('p', 2), ('s', 4), ('m', 1)] |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
452 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
453 |
When a letter is first encountered, it is missing from the mapping, so the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
454 |
:attr:`default_factory` function calls :func:`int` to supply a default count of |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
455 |
zero. The increment operation then builds up the count for each letter. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
456 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
457 |
The function :func:`int` which always returns zero is just a special case of |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
458 |
constant functions. A faster and more flexible way to create constant functions |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
459 |
is to use :func:`itertools.repeat` which can supply any constant value (not just |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
460 |
zero): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
461 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
462 |
>>> def constant_factory(value): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
463 |
... return itertools.repeat(value).next |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
464 |
>>> d = defaultdict(constant_factory('<missing>')) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
465 |
>>> d.update(name='John', action='ran') |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
466 |
>>> '%(name)s %(action)s to %(object)s' % d |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
467 |
'John ran to <missing>' |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
468 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
469 |
Setting the :attr:`default_factory` to :class:`set` makes the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
470 |
:class:`defaultdict` useful for building a dictionary of sets: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
471 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
472 |
>>> s = [('red', 1), ('blue', 2), ('red', 3), ('blue', 4), ('red', 1), ('blue', 4)] |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
473 |
>>> d = defaultdict(set) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
474 |
>>> for k, v in s: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
475 |
... d[k].add(v) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
476 |
... |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
477 |
>>> d.items() |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
478 |
[('blue', set([2, 4])), ('red', set([1, 3]))] |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
479 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
480 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
481 |
.. _named-tuple-factory: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
482 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
483 |
:func:`namedtuple` Factory Function for Tuples with Named Fields |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
484 |
---------------------------------------------------------------- |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
485 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
486 |
Named tuples assign meaning to each position in a tuple and allow for more readable, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
487 |
self-documenting code. They can be used wherever regular tuples are used, and |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
488 |
they add the ability to access fields by name instead of position index. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
489 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
490 |
.. function:: namedtuple(typename, fieldnames, [verbose]) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
491 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
492 |
Returns a new tuple subclass named *typename*. The new subclass is used to |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
493 |
create tuple-like objects that have fields accessible by attribute lookup as |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
494 |
well as being indexable and iterable. Instances of the subclass also have a |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
495 |
helpful docstring (with typename and fieldnames) and a helpful :meth:`__repr__` |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
496 |
method which lists the tuple contents in a ``name=value`` format. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
497 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
498 |
The *fieldnames* are a single string with each fieldname separated by whitespace |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
499 |
and/or commas, for example ``'x y'`` or ``'x, y'``. Alternatively, *fieldnames* |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
500 |
can be a sequence of strings such as ``['x', 'y']``. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
501 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
502 |
Any valid Python identifier may be used for a fieldname except for names |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
503 |
starting with an underscore. Valid identifiers consist of letters, digits, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
504 |
and underscores but do not start with a digit or underscore and cannot be |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
505 |
a :mod:`keyword` such as *class*, *for*, *return*, *global*, *pass*, *print*, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
506 |
or *raise*. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
507 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
508 |
If *verbose* is true, the class definition is printed just before being built. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
509 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
510 |
Named tuple instances do not have per-instance dictionaries, so they are |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
511 |
lightweight and require no more memory than regular tuples. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
512 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
513 |
.. versionadded:: 2.6 |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
514 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
515 |
Example: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
516 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
517 |
.. doctest:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
518 |
:options: +NORMALIZE_WHITESPACE |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
519 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
520 |
>>> Point = namedtuple('Point', 'x y', verbose=True) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
521 |
class Point(tuple): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
522 |
'Point(x, y)' |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
523 |
<BLANKLINE> |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
524 |
__slots__ = () |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
525 |
<BLANKLINE> |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
526 |
_fields = ('x', 'y') |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
527 |
<BLANKLINE> |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
528 |
def __new__(cls, x, y): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
529 |
return tuple.__new__(cls, (x, y)) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
530 |
<BLANKLINE> |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
531 |
@classmethod |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
532 |
def _make(cls, iterable, new=tuple.__new__, len=len): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
533 |
'Make a new Point object from a sequence or iterable' |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
534 |
result = new(cls, iterable) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
535 |
if len(result) != 2: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
536 |
raise TypeError('Expected 2 arguments, got %d' % len(result)) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
537 |
return result |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
538 |
<BLANKLINE> |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
539 |
def __repr__(self): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
540 |
return 'Point(x=%r, y=%r)' % self |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
541 |
<BLANKLINE> |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
542 |
def _asdict(t): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
543 |
'Return a new dict which maps field names to their values' |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
544 |
return {'x': t[0], 'y': t[1]} |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
545 |
<BLANKLINE> |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
546 |
def _replace(self, **kwds): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
547 |
'Return a new Point object replacing specified fields with new values' |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
548 |
result = self._make(map(kwds.pop, ('x', 'y'), self)) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
549 |
if kwds: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
550 |
raise ValueError('Got unexpected field names: %r' % kwds.keys()) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
551 |
return result |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
552 |
<BLANKLINE> |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
553 |
def __getnewargs__(self): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
554 |
return tuple(self) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
555 |
<BLANKLINE> |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
556 |
x = property(itemgetter(0)) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
557 |
y = property(itemgetter(1)) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
558 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
559 |
>>> p = Point(11, y=22) # instantiate with positional or keyword arguments |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
560 |
>>> p[0] + p[1] # indexable like the plain tuple (11, 22) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
561 |
33 |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
562 |
>>> x, y = p # unpack like a regular tuple |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
563 |
>>> x, y |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
564 |
(11, 22) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
565 |
>>> p.x + p.y # fields also accessible by name |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
566 |
33 |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
567 |
>>> p # readable __repr__ with a name=value style |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
568 |
Point(x=11, y=22) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
569 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
570 |
Named tuples are especially useful for assigning field names to result tuples returned |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
571 |
by the :mod:`csv` or :mod:`sqlite3` modules:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
572 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
573 |
EmployeeRecord = namedtuple('EmployeeRecord', 'name, age, title, department, paygrade') |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
574 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
575 |
import csv |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
576 |
for emp in map(EmployeeRecord._make, csv.reader(open("employees.csv", "rb"))): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
577 |
print emp.name, emp.title |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
578 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
579 |
import sqlite3 |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
580 |
conn = sqlite3.connect('/companydata') |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
581 |
cursor = conn.cursor() |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
582 |
cursor.execute('SELECT name, age, title, department, paygrade FROM employees') |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
583 |
for emp in map(EmployeeRecord._make, cursor.fetchall()): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
584 |
print emp.name, emp.title |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
585 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
586 |
In addition to the methods inherited from tuples, named tuples support |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
587 |
three additional methods and one attribute. To prevent conflicts with |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
588 |
field names, the method and attribute names start with an underscore. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
589 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
590 |
.. method:: somenamedtuple._make(iterable) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
591 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
592 |
Class method that makes a new instance from an existing sequence or iterable. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
593 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
594 |
.. doctest:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
595 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
596 |
>>> t = [11, 22] |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
597 |
>>> Point._make(t) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
598 |
Point(x=11, y=22) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
599 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
600 |
.. method:: somenamedtuple._asdict() |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
601 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
602 |
Return a new dict which maps field names to their corresponding values:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
603 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
604 |
>>> p._asdict() |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
605 |
{'x': 11, 'y': 22} |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
606 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
607 |
.. method:: somenamedtuple._replace(kwargs) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
608 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
609 |
Return a new instance of the named tuple replacing specified fields with new |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
610 |
values: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
611 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
612 |
:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
613 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
614 |
>>> p = Point(x=11, y=22) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
615 |
>>> p._replace(x=33) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
616 |
Point(x=33, y=22) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
617 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
618 |
>>> for partnum, record in inventory.items(): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
619 |
... inventory[partnum] = record._replace(price=newprices[partnum], timestamp=time.now()) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
620 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
621 |
.. attribute:: somenamedtuple._fields |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
622 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
623 |
Tuple of strings listing the field names. Useful for introspection |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
624 |
and for creating new named tuple types from existing named tuples. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
625 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
626 |
.. doctest:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
627 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
628 |
>>> p._fields # view the field names |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
629 |
('x', 'y') |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
630 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
631 |
>>> Color = namedtuple('Color', 'red green blue') |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
632 |
>>> Pixel = namedtuple('Pixel', Point._fields + Color._fields) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
633 |
>>> Pixel(11, 22, 128, 255, 0) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
634 |
Pixel(x=11, y=22, red=128, green=255, blue=0) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
635 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
636 |
To retrieve a field whose name is stored in a string, use the :func:`getattr` |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
637 |
function: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
638 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
639 |
>>> getattr(p, 'x') |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
640 |
11 |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
641 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
642 |
To convert a dictionary to a named tuple, use the double-star-operator [#]_: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
643 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
644 |
>>> d = {'x': 11, 'y': 22} |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
645 |
>>> Point(**d) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
646 |
Point(x=11, y=22) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
647 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
648 |
Since a named tuple is a regular Python class, it is easy to add or change |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
649 |
functionality with a subclass. Here is how to add a calculated field and |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
650 |
a fixed-width print format: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
651 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
652 |
>>> class Point(namedtuple('Point', 'x y')): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
653 |
... __slots__ = () |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
654 |
... @property |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
655 |
... def hypot(self): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
656 |
... return (self.x ** 2 + self.y ** 2) ** 0.5 |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
657 |
... def __str__(self): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
658 |
... return 'Point: x=%6.3f y=%6.3f hypot=%6.3f' % (self.x, self.y, self.hypot) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
659 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
660 |
>>> for p in Point(3, 4), Point(14, 5/7.): |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
661 |
... print p |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
662 |
Point: x= 3.000 y= 4.000 hypot= 5.000 |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
663 |
Point: x=14.000 y= 0.714 hypot=14.018 |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
664 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
665 |
The subclass shown above sets ``__slots__`` to an empty tuple. This keeps |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
666 |
keep memory requirements low by preventing the creation of instance dictionaries. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
667 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
668 |
Subclassing is not useful for adding new, stored fields. Instead, simply |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
669 |
create a new named tuple type from the :attr:`_fields` attribute: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
670 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
671 |
>>> Point3D = namedtuple('Point3D', Point._fields + ('z',)) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
672 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
673 |
Default values can be implemented by using :meth:`_replace` to |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
674 |
customize a prototype instance: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
675 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
676 |
>>> Account = namedtuple('Account', 'owner balance transaction_count') |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
677 |
>>> default_account = Account('<owner name>', 0.0, 0) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
678 |
>>> johns_account = default_account._replace(owner='John') |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
679 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
680 |
Enumerated constants can be implemented with named tuples, but it is simpler |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
681 |
and more efficient to use a simple class declaration: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
682 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
683 |
>>> Status = namedtuple('Status', 'open pending closed')._make(range(3)) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
684 |
>>> Status.open, Status.pending, Status.closed |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
685 |
(0, 1, 2) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
686 |
>>> class Status: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
687 |
... open, pending, closed = range(3) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
688 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
689 |
.. rubric:: Footnotes |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
690 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
691 |
.. [#] For information on the double-star-operator see |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
692 |
:ref:`tut-unpacking-arguments` and :ref:`calls`. |