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Note that the _asdict() method is outdated

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Doc/library/collections.rst
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...@@ -2,15 +2,15 @@ ...@@ -2,15 +2,15 @@
========================================== ==========================================
.. module:: collections .. module:: collections
:synopsis: Container datatypes :synopsis: Container datatypes
.. moduleauthor:: Raymond Hettinger <python@rcn.com> .. moduleauthor:: Raymond Hettinger <python@rcn.com>
.. sectionauthor:: Raymond Hettinger <python@rcn.com> .. sectionauthor:: Raymond Hettinger <python@rcn.com>
.. testsetup:: * .. testsetup:: *
from collections import * from collections import *
import itertools import itertools
__name__ = '<doctest>' __name__ = '<doctest>'
**Source code:** :source:`Lib/collections/__init__.py` **Source code:** :source:`Lib/collections/__init__.py`
...@@ -33,9 +33,9 @@ Python's general purpose built-in containers, :class:`dict`, :class:`list`, ...@@ -33,9 +33,9 @@ Python's general purpose built-in containers, :class:`dict`, :class:`list`,
===================== ==================================================================== ===================== ====================================================================
.. versionchanged:: 3.3 .. versionchanged:: 3.3
Moved :ref:`collections-abstract-base-classes` to the :mod:`collections.abc` module. Moved :ref:`collections-abstract-base-classes` to the :mod:`collections.abc` module.
For backwards compatibility, they continue to be visible in this module For backwards compatibility, they continue to be visible in this module
as well. as well.
:class:`ChainMap` objects :class:`ChainMap` objects
...@@ -51,105 +51,105 @@ The class can be used to simulate nested scopes and is useful in templating. ...@@ -51,105 +51,105 @@ The class can be used to simulate nested scopes and is useful in templating.
.. class:: ChainMap(*maps) .. class:: ChainMap(*maps)
A :class:`ChainMap` groups multiple dicts or other mappings together to A :class:`ChainMap` groups multiple dicts or other mappings together to
create a single, updateable view. If no *maps* are specified, a single empty create a single, updateable view. If no *maps* are specified, a single empty
dictionary is provided so that a new chain always has at least one mapping. dictionary is provided so that a new chain always has at least one mapping.
The underlying mappings are stored in a list. That list is public and can The underlying mappings are stored in a list. That list is public and can
accessed or updated using the *maps* attribute. There is no other state. accessed or updated using the *maps* attribute. There is no other state.
Lookups search the underlying mappings successively until a key is found. In Lookups search the underlying mappings successively until a key is found. In
contrast, writes, updates, and deletions only operate on the first mapping. contrast, writes, updates, and deletions only operate on the first mapping.
A :class:`ChainMap` incorporates the underlying mappings by reference. So, if A :class:`ChainMap` incorporates the underlying mappings by reference. So, if
one of the underlying mappings gets updated, those changes will be reflected one of the underlying mappings gets updated, those changes will be reflected
in :class:`ChainMap`. in :class:`ChainMap`.
All of the usual dictionary methods are supported. In addition, there is a All of the usual dictionary methods are supported. In addition, there is a
*maps* attribute, a method for creating new subcontexts, and a property for *maps* attribute, a method for creating new subcontexts, and a property for
accessing all but the first mapping: accessing all but the first mapping:
.. attribute:: maps .. attribute:: maps
A user updateable list of mappings. The list is ordered from A user updateable list of mappings. The list is ordered from
first-searched to last-searched. It is the only stored state and can first-searched to last-searched. It is the only stored state and can
be modified to change which mappings are searched. The list should be modified to change which mappings are searched. The list should
always contain at least one mapping. always contain at least one mapping.
.. method:: new_child() .. method:: new_child()
Returns a new :class:`ChainMap` containing a new :class:`dict` followed by Returns a new :class:`ChainMap` containing a new :class:`dict` followed by
all of the maps in the current instance. A call to ``d.new_child()`` is all of the maps in the current instance. A call to ``d.new_child()`` is
equivalent to: ``ChainMap({}, *d.maps)``. This method is used for equivalent to: ``ChainMap({}, *d.maps)``. This method is used for
creating subcontexts that can be updated without altering values in any creating subcontexts that can be updated without altering values in any
of the parent mappings. of the parent mappings.
.. method:: parents() .. method:: parents()
Returns a new :class:`ChainMap` containing all of the maps in the current Returns a new :class:`ChainMap` containing all of the maps in the current
instance except the first one. This is useful for skipping the first map instance except the first one. This is useful for skipping the first map
in the search. The use-cases are similar to those for the in the search. The use-cases are similar to those for the
:keyword:`nonlocal` keyword used in :term:`nested scopes <nested scope>`. :keyword:`nonlocal` keyword used in :term:`nested scopes <nested scope>`.
The use-cases also parallel those for the builtin :func:`super` function. The use-cases also parallel those for the builtin :func:`super` function.
A reference to ``d.parents`` is equivalent to: ``ChainMap(*d.maps[1:])``. A reference to ``d.parents`` is equivalent to: ``ChainMap(*d.maps[1:])``.
Example of simulating Python's internal lookup chain:: Example of simulating Python's internal lookup chain::
import builtins import builtins
pylookup = ChainMap(locals(), globals(), vars(builtins)) pylookup = ChainMap(locals(), globals(), vars(builtins))
Example of letting user specified values take precedence over environment Example of letting user specified values take precedence over environment
variables which in turn take precedence over default values:: variables which in turn take precedence over default values::
import os, argparse import os, argparse
defaults = {'color': 'red', 'user': guest} defaults = {'color': 'red', 'user': guest}
parser = argparse.ArgumentParser() parser = argparse.ArgumentParser()
parser.add_argument('-u', '--user') parser.add_argument('-u', '--user')
parser.add_argument('-c', '--color') parser.add_argument('-c', '--color')
user_specified = vars(parser.parse_args()) user_specified = vars(parser.parse_args())
combined = ChainMap(user_specified, os.environ, defaults) combined = ChainMap(user_specified, os.environ, defaults)
Example patterns for using the :class:`ChainMap` class to simulate nested Example patterns for using the :class:`ChainMap` class to simulate nested
contexts:: contexts::
c = ChainMap() # Create root context c = ChainMap() # Create root context
d = c.new_child() # Create nested child context d = c.new_child() # Create nested child context
e = c.new_child() # Child of c, independent from d e = c.new_child() # Child of c, independent from d
e.maps[0] # Current context dictionary -- like Python's locals() e.maps[0] # Current context dictionary -- like Python's locals()
e.maps[-1] # Root context -- like Python's globals() e.maps[-1] # Root context -- like Python's globals()
e.parents # Enclosing context chain -- like Python's nonlocals e.parents # Enclosing context chain -- like Python's nonlocals
d['x'] # Get first key in the chain of contexts d['x'] # Get first key in the chain of contexts
d['x'] = 1 # Set value in current context d['x'] = 1 # Set value in current context
del['x'] # Delete from current context del['x'] # Delete from current context
list(d) # All nested values list(d) # All nested values
k in d # Check all nested values k in d # Check all nested values
len(d) # Number of nested values len(d) # Number of nested values
d.items() # All nested items d.items() # All nested items
dict(d) # Flatten into a regular dictionary dict(d) # Flatten into a regular dictionary
.. seealso:: .. seealso::
* The `MultiContext class * The `MultiContext class
<http://svn.enthought.com/svn/enthought/CodeTools/trunk/enthought/contexts/multi_context.py>`_ <http://svn.enthought.com/svn/enthought/CodeTools/trunk/enthought/contexts/multi_context.py>`_
in the Enthought `CodeTools package in the Enthought `CodeTools package
<https://github.com/enthought/codetools>`_ has options to support <https://github.com/enthought/codetools>`_ has options to support
writing to any mapping in the chain. writing to any mapping in the chain.
* Django's `Context class * Django's `Context class
<http://code.djangoproject.com/browser/django/trunk/django/template/context.py>`_ <http://code.djangoproject.com/browser/django/trunk/django/template/context.py>`_
for templating is a read-only chain of mappings. It also features for templating is a read-only chain of mappings. It also features
pushing and popping of contexts similar to the pushing and popping of contexts similar to the
:meth:`~collections.ChainMap.new_child` method and the :meth:`~collections.ChainMap.new_child` method and the
:meth:`~collections.ChainMap.parents` property. :meth:`~collections.ChainMap.parents` property.
* The `Nested Contexts recipe * The `Nested Contexts recipe
<http://code.activestate.com/recipes/577434/>`_ has options to control <http://code.activestate.com/recipes/577434/>`_ has options to control
whether writes and other mutations apply only to the first mapping or to whether writes and other mutations apply only to the first mapping or to
any mapping in the chain. any mapping in the chain.
* A `greatly simplified read-only version of Chainmap * A `greatly simplified read-only version of Chainmap
<http://code.activestate.com/recipes/305268/>`_. <http://code.activestate.com/recipes/305268/>`_.
:class:`Counter` objects :class:`Counter` objects
...@@ -174,85 +174,85 @@ For example:: ...@@ -174,85 +174,85 @@ For example::
.. class:: Counter([iterable-or-mapping]) .. class:: Counter([iterable-or-mapping])
A :class:`Counter` is a :class:`dict` subclass for counting hashable objects. A :class:`Counter` is a :class:`dict` subclass for counting hashable objects.
It is an unordered collection where elements are stored as dictionary keys It is an unordered collection where elements are stored as dictionary keys
and their counts are stored as dictionary values. Counts are allowed to be and their counts are stored as dictionary values. Counts are allowed to be
any integer value including zero or negative counts. The :class:`Counter` any integer value including zero or negative counts. The :class:`Counter`
class is similar to bags or multisets in other languages. class is similar to bags or multisets in other languages.
Elements are counted from an *iterable* or initialized from another Elements are counted from an *iterable* or initialized from another
*mapping* (or counter): *mapping* (or counter):
>>> c = Counter() # a new, empty counter >>> c = Counter() # a new, empty counter
>>> c = Counter('gallahad') # a new counter from an iterable >>> c = Counter('gallahad') # a new counter from an iterable
>>> c = Counter({'red': 4, 'blue': 2}) # a new counter from a mapping >>> c = Counter({'red': 4, 'blue': 2}) # a new counter from a mapping
>>> c = Counter(cats=4, dogs=8) # a new counter from keyword args >>> c = Counter(cats=4, dogs=8) # a new counter from keyword args
Counter objects have a dictionary interface except that they return a zero Counter objects have a dictionary interface except that they return a zero
count for missing items instead of raising a :exc:`KeyError`: count for missing items instead of raising a :exc:`KeyError`:
>>> c = Counter(['eggs', 'ham']) >>> c = Counter(['eggs', 'ham'])
>>> c['bacon'] # count of a missing element is zero >>> c['bacon'] # count of a missing element is zero
0 0
Setting a count to zero does not remove an element from a counter. Setting a count to zero does not remove an element from a counter.
Use ``del`` to remove it entirely: Use ``del`` to remove it entirely:
>>> c['sausage'] = 0 # counter entry with a zero count >>> c['sausage'] = 0 # counter entry with a zero count
>>> del c['sausage'] # del actually removes the entry >>> del c['sausage'] # del actually removes the entry
.. versionadded:: 3.1 .. versionadded:: 3.1
Counter objects support three methods beyond those available for all Counter objects support three methods beyond those available for all
dictionaries: dictionaries:
.. method:: elements() .. method:: elements()
Return an iterator over elements repeating each as many times as its Return an iterator over elements repeating each as many times as its
count. Elements are returned in arbitrary order. If an element's count count. Elements are returned in arbitrary order. If an element's count
is less than one, :meth:`elements` will ignore it. is less than one, :meth:`elements` will ignore it.
>>> c = Counter(a=4, b=2, c=0, d=-2) >>> c = Counter(a=4, b=2, c=0, d=-2)
>>> list(c.elements()) >>> list(c.elements())
['a', 'a', 'a', 'a', 'b', 'b'] ['a', 'a', 'a', 'a', 'b', 'b']
.. method:: most_common([n]) .. method:: most_common([n])
Return a list of the *n* most common elements and their counts from the Return a list of the *n* most common elements and their counts from the
most common to the least. If *n* is not specified, :func:`most_common` most common to the least. If *n* is not specified, :func:`most_common`
returns *all* elements in the counter. Elements with equal counts are returns *all* elements in the counter. Elements with equal counts are
ordered arbitrarily: ordered arbitrarily:
>>> Counter('abracadabra').most_common(3) >>> Counter('abracadabra').most_common(3)
[('a', 5), ('r', 2), ('b', 2)] [('a', 5), ('r', 2), ('b', 2)]
.. method:: subtract([iterable-or-mapping]) .. method:: subtract([iterable-or-mapping])
Elements are subtracted from an *iterable* or from another *mapping* Elements are subtracted from an *iterable* or from another *mapping*
(or counter). Like :meth:`dict.update` but subtracts counts instead (or counter). Like :meth:`dict.update` but subtracts counts instead
of replacing them. Both inputs and outputs may be zero or negative. of replacing them. Both inputs and outputs may be zero or negative.
>>> c = Counter(a=4, b=2, c=0, d=-2) >>> c = Counter(a=4, b=2, c=0, d=-2)
>>> d = Counter(a=1, b=2, c=3, d=4) >>> d = Counter(a=1, b=2, c=3, d=4)
>>> c.subtract(d) >>> c.subtract(d)
Counter({'a': 3, 'b': 0, 'c': -3, 'd': -6}) Counter({'a': 3, 'b': 0, 'c': -3, 'd': -6})
.. versionadded:: 3.2 .. versionadded:: 3.2
The usual dictionary methods are available for :class:`Counter` objects The usual dictionary methods are available for :class:`Counter` objects
except for two which work differently for counters. except for two which work differently for counters.
.. method:: fromkeys(iterable) .. method:: fromkeys(iterable)
This class method is not implemented for :class:`Counter` objects. This class method is not implemented for :class:`Counter` objects.
.. method:: update([iterable-or-mapping]) .. method:: update([iterable-or-mapping])
Elements are counted from an *iterable* or added-in from another Elements are counted from an *iterable* or added-in from another
*mapping* (or counter). Like :meth:`dict.update` but adds counts *mapping* (or counter). Like :meth:`dict.update` but adds counts
instead of replacing them. Also, the *iterable* is expected to be a instead of replacing them. Also, the *iterable* is expected to be a
sequence of elements, not a sequence of ``(key, value)`` pairs. sequence of elements, not a sequence of ``(key, value)`` pairs.
Common patterns for working with :class:`Counter` objects:: Common patterns for working with :class:`Counter` objects::
...@@ -294,57 +294,57 @@ or subtracting from an empty counter. ...@@ -294,57 +294,57 @@ or subtracting from an empty counter.
Counter({'b': 4}) Counter({'b': 4})
.. versionadded:: 3.3 .. versionadded:: 3.3
Added support for unary plus, unary minus, and in-place multiset operations. Added support for unary plus, unary minus, and in-place multiset operations.
.. note:: .. note::
Counters were primarily designed to work with positive integers to represent Counters were primarily designed to work with positive integers to represent
running counts; however, care was taken to not unnecessarily preclude use running counts; however, care was taken to not unnecessarily preclude use
cases needing other types or negative values. To help with those use cases, cases needing other types or negative values. To help with those use cases,
this section documents the minimum range and type restrictions. this section documents the minimum range and type restrictions.
* The :class:`Counter` class itself is a dictionary subclass with no * The :class:`Counter` class itself is a dictionary subclass with no
restrictions on its keys and values. The values are intended to be numbers restrictions on its keys and values. The values are intended to be numbers
representing counts, but you *could* store anything in the value field. representing counts, but you *could* store anything in the value field.
* The :meth:`most_common` method requires only that the values be orderable. * The :meth:`most_common` method requires only that the values be orderable.
* For in-place operations such as ``c[key] += 1``, the value type need only * For in-place operations such as ``c[key] += 1``, the value type need only
support addition and subtraction. So fractions, floats, and decimals would support addition and subtraction. So fractions, floats, and decimals would
work and negative values are supported. The same is also true for work and negative values are supported. The same is also true for
:meth:`update` and :meth:`subtract` which allow negative and zero values :meth:`update` and :meth:`subtract` which allow negative and zero values
for both inputs and outputs. for both inputs and outputs.
* The multiset methods are designed only for use cases with positive values. * The multiset methods are designed only for use cases with positive values.
The inputs may be negative or zero, but only outputs with positive values The inputs may be negative or zero, but only outputs with positive values
are created. There are no type restrictions, but the value type needs to are created. There are no type restrictions, but the value type needs to
support addition, subtraction, and comparison. support addition, subtraction, and comparison.
* The :meth:`elements` method requires integer counts. It ignores zero and * The :meth:`elements` method requires integer counts. It ignores zero and
negative counts. negative counts.
.. seealso:: .. seealso::
* `Counter class <http://code.activestate.com/recipes/576611/>`_ * `Counter class <http://code.activestate.com/recipes/576611/>`_
adapted for Python 2.5 and an early `Bag recipe adapted for Python 2.5 and an early `Bag recipe
<http://code.activestate.com/recipes/259174/>`_ for Python 2.4. <http://code.activestate.com/recipes/259174/>`_ for Python 2.4.
* `Bag class <http://www.gnu.org/software/smalltalk/manual-base/html_node/Bag.html>`_ * `Bag class <http://www.gnu.org/software/smalltalk/manual-base/html_node/Bag.html>`_
in Smalltalk. in Smalltalk.
* Wikipedia entry for `Multisets <http://en.wikipedia.org/wiki/Multiset>`_. * Wikipedia entry for `Multisets <http://en.wikipedia.org/wiki/Multiset>`_.
* `C++ multisets <http://www.demo2s.com/Tutorial/Cpp/0380__set-multiset/Catalog0380__set-multiset.htm>`_ * `C++ multisets <http://www.demo2s.com/Tutorial/Cpp/0380__set-multiset/Catalog0380__set-multiset.htm>`_
tutorial with examples. tutorial with examples.
* For mathematical operations on multisets and their use cases, see * For mathematical operations on multisets and their use cases, see
*Knuth, Donald. The Art of Computer Programming Volume II, *Knuth, Donald. The Art of Computer Programming Volume II,
Section 4.6.3, Exercise 19*. Section 4.6.3, Exercise 19*.
* To enumerate all distinct multisets of a given size over a given set of * To enumerate all distinct multisets of a given size over a given set of
elements, see :func:`itertools.combinations_with_replacement`. elements, see :func:`itertools.combinations_with_replacement`.
map(Counter, combinations_with_replacement('ABC', 2)) --> AA AB AC BB BC CC map(Counter, combinations_with_replacement('ABC', 2)) --> AA AB AC BB BC CC
:class:`deque` objects :class:`deque` objects
...@@ -352,105 +352,105 @@ or subtracting from an empty counter. ...@@ -352,105 +352,105 @@ or subtracting from an empty counter.
.. class:: deque([iterable, [maxlen]]) .. class:: deque([iterable, [maxlen]])
Returns a new deque object initialized left-to-right (using :meth:`append`) with Returns a new deque object initialized left-to-right (using :meth:`append`) with
data from *iterable*. If *iterable* is not specified, the new deque is empty. data from *iterable*. If *iterable* is not specified, the new deque is empty.
Deques are a generalization of stacks and queues (the name is pronounced "deck" Deques are a generalization of stacks and queues (the name is pronounced "deck"
and is short for "double-ended queue"). Deques support thread-safe, memory and is short for "double-ended queue"). Deques support thread-safe, memory
efficient appends and pops from either side of the deque with approximately the efficient appends and pops from either side of the deque with approximately the
same O(1) performance in either direction. same O(1) performance in either direction.
Though :class:`list` objects support similar operations, they are optimized for Though :class:`list` objects support similar operations, they are optimized for
fast fixed-length operations and incur O(n) memory movement costs for fast fixed-length operations and incur O(n) memory movement costs for
``pop(0)`` and ``insert(0, v)`` operations which change both the size and ``pop(0)`` and ``insert(0, v)`` operations which change both the size and
position of the underlying data representation. position of the underlying data representation.
If *maxlen* is not specified or is *None*, deques may grow to an If *maxlen* is not specified or is *None*, deques may grow to an
arbitrary length. Otherwise, the deque is bounded to the specified maximum arbitrary length. Otherwise, the deque is bounded to the specified maximum
length. Once a bounded length deque is full, when new items are added, a length. Once a bounded length deque is full, when new items are added, a
corresponding number of items are discarded from the opposite end. Bounded corresponding number of items are discarded from the opposite end. Bounded
length deques provide functionality similar to the ``tail`` filter in length deques provide functionality similar to the ``tail`` filter in
Unix. They are also useful for tracking transactions and other pools of data Unix. They are also useful for tracking transactions and other pools of data
where only the most recent activity is of interest. where only the most recent activity is of interest.
Deque objects support the following methods: Deque objects support the following methods:
.. method:: append(x) .. method:: append(x)
Add *x* to the right side of the deque. Add *x* to the right side of the deque.
.. method:: appendleft(x) .. method:: appendleft(x)
Add *x* to the left side of the deque. Add *x* to the left side of the deque.
.. method:: clear() .. method:: clear()
Remove all elements from the deque leaving it with length 0. Remove all elements from the deque leaving it with length 0.
.. method:: count(x) .. method:: count(x)
Count the number of deque elements equal to *x*. Count the number of deque elements equal to *x*.
.. versionadded:: 3.2 .. versionadded:: 3.2
.. method:: extend(iterable) .. method:: extend(iterable)
Extend the right side of the deque by appending elements from the iterable Extend the right side of the deque by appending elements from the iterable
argument. argument.
.. method:: extendleft(iterable) .. method:: extendleft(iterable)
Extend the left side of the deque by appending elements from *iterable*. Extend the left side of the deque by appending elements from *iterable*.
Note, the series of left appends results in reversing the order of Note, the series of left appends results in reversing the order of
elements in the iterable argument. elements in the iterable argument.
.. method:: pop() .. method:: pop()
Remove and return an element from the right side of the deque. If no Remove and return an element from the right side of the deque. If no
elements are present, raises an :exc:`IndexError`. elements are present, raises an :exc:`IndexError`.
.. method:: popleft() .. method:: popleft()
Remove and return an element from the left side of the deque. If no Remove and return an element from the left side of the deque. If no
elements are present, raises an :exc:`IndexError`. elements are present, raises an :exc:`IndexError`.
.. method:: remove(value) .. method:: remove(value)
Removed the first occurrence of *value*. If not found, raises a Removed the first occurrence of *value*. If not found, raises a
:exc:`ValueError`. :exc:`ValueError`.
.. method:: reverse() .. method:: reverse()
Reverse the elements of the deque in-place and then return ``None``. Reverse the elements of the deque in-place and then return ``None``.
.. versionadded:: 3.2 .. versionadded:: 3.2
.. method:: rotate(n) .. method:: rotate(n)
Rotate the deque *n* steps to the right. If *n* is negative, rotate to Rotate the deque *n* steps to the right. If *n* is negative, rotate to
the left. Rotating one step to the right is equivalent to: the left. Rotating one step to the right is equivalent to:
``d.appendleft(d.pop())``. ``d.appendleft(d.pop())``.
Deque objects also provide one read-only attribute: Deque objects also provide one read-only attribute:
.. attribute:: maxlen .. attribute:: maxlen
Maximum size of a deque or *None* if unbounded. Maximum size of a deque or *None* if unbounded.
.. versionadded:: 3.1 .. versionadded:: 3.1
In addition to the above, deques support iteration, pickling, ``len(d)``, In addition to the above, deques support iteration, pickling, ``len(d)``,
...@@ -463,56 +463,56 @@ Example: ...@@ -463,56 +463,56 @@ Example:
.. doctest:: .. doctest::
>>> from collections import deque >>> from collections import deque
>>> d = deque('ghi') # make a new deque with three items >>> d = deque('ghi') # make a new deque with three items
>>> for elem in d: # iterate over the deque's elements >>> for elem in d: # iterate over the deque's elements
... print(elem.upper()) ... print(elem.upper())
G G
H H
I I
>>> d.append('j') # add a new entry to the right side >>> d.append('j') # add a new entry to the right side
>>> d.appendleft('f') # add a new entry to the left side >>> d.appendleft('f') # add a new entry to the left side
>>> d # show the representation of the deque >>> d # show the representation of the deque
deque(['f', 'g', 'h', 'i', 'j']) deque(['f', 'g', 'h', 'i', 'j'])
>>> d.pop() # return and remove the rightmost item >>> d.pop() # return and remove the rightmost item
'j' 'j'
>>> d.popleft() # return and remove the leftmost item >>> d.popleft() # return and remove the leftmost item
'f' 'f'
>>> list(d) # list the contents of the deque >>> list(d) # list the contents of the deque
['g', 'h', 'i'] ['g', 'h', 'i']
>>> d[0] # peek at leftmost item >>> d[0] # peek at leftmost item
'g' 'g'
>>> d[-1] # peek at rightmost item >>> d[-1] # peek at rightmost item
'i' 'i'
>>> list(reversed(d)) # list the contents of a deque in reverse >>> list(reversed(d)) # list the contents of a deque in reverse
['i', 'h', 'g'] ['i', 'h', 'g']
>>> 'h' in d # search the deque >>> 'h' in d # search the deque
True True
>>> d.extend('jkl') # add multiple elements at once >>> d.extend('jkl') # add multiple elements at once
>>> d >>> d
deque(['g', 'h', 'i', 'j', 'k', 'l']) deque(['g', 'h', 'i', 'j', 'k', 'l'])
>>> d.rotate(1) # right rotation >>> d.rotate(1) # right rotation
>>> d >>> d
deque(['l', 'g', 'h', 'i', 'j', 'k']) deque(['l', 'g', 'h', 'i', 'j', 'k'])
>>> d.rotate(-1) # left rotation >>> d.rotate(-1) # left rotation
>>> d >>> d
deque(['g', 'h', 'i', 'j', 'k', 'l']) deque(['g', 'h', 'i', 'j', 'k', 'l'])
>>> deque(reversed(d)) # make a new deque in reverse order >>> deque(reversed(d)) # make a new deque in reverse order
deque(['l', 'k', 'j', 'i', 'h', 'g']) deque(['l', 'k', 'j', 'i', 'h', 'g'])
>>> d.clear() # empty the deque >>> d.clear() # empty the deque
>>> d.pop() # cannot pop from an empty deque >>> d.pop() # cannot pop from an empty deque
Traceback (most recent call last): Traceback (most recent call last):
File "<pyshell#6>", line 1, in -toplevel- File "<pyshell#6>", line 1, in -toplevel-
d.pop() d.pop()
IndexError: pop from an empty deque IndexError: pop from an empty deque
>>> d.extendleft('abc') # extendleft() reverses the input order >>> d.extendleft('abc') # extendleft() reverses the input order
>>> d >>> d
deque(['c', 'b', 'a']) deque(['c', 'b', 'a'])
:class:`deque` Recipes :class:`deque` Recipes
...@@ -523,10 +523,10 @@ This section shows various approaches to working with deques. ...@@ -523,10 +523,10 @@ This section shows various approaches to working with deques.
Bounded length deques provide functionality similar to the ``tail`` filter Bounded length deques provide functionality similar to the ``tail`` filter
in Unix:: in Unix::
def tail(filename, n=10): def tail(filename, n=10):
'Return the last n lines of a file' 'Return the last n lines of a file'
with open(filename) as f: with open(filename) as f:
return deque(f, n) return deque(f, n)
Another approach to using deques is to maintain a sequence of recently Another approach to using deques is to maintain a sequence of recently
added elements by appending to the right and popping to the left:: added elements by appending to the right and popping to the left::
...@@ -547,10 +547,10 @@ The :meth:`rotate` method provides a way to implement :class:`deque` slicing and ...@@ -547,10 +547,10 @@ The :meth:`rotate` method provides a way to implement :class:`deque` slicing and
deletion. For example, a pure Python implementation of ``del d[n]`` relies on deletion. For example, a pure Python implementation of ``del d[n]`` relies on
the :meth:`rotate` method to position elements to be popped:: the :meth:`rotate` method to position elements to be popped::
def delete_nth(d, n): def delete_nth(d, n):
d.rotate(-n) d.rotate(-n)
d.popleft() d.popleft()
d.rotate(n) d.rotate(n)
To implement :class:`deque` slicing, use a similar approach applying To implement :class:`deque` slicing, use a similar approach applying
:meth:`rotate` to bring a target element to the left side of the deque. Remove :meth:`rotate` to bring a target element to the left side of the deque. Remove
...@@ -566,50 +566,50 @@ stack manipulations such as ``dup``, ``drop``, ``swap``, ``over``, ``pick``, ...@@ -566,50 +566,50 @@ stack manipulations such as ``dup``, ``drop``, ``swap``, ``over``, ``pick``,
.. class:: defaultdict([default_factory[, ...]]) .. class:: defaultdict([default_factory[, ...]])
Returns a new dictionary-like object. :class:`defaultdict` is a subclass of the Returns a new dictionary-like object. :class:`defaultdict` is a subclass of the
built-in :class:`dict` class. It overrides one method and adds one writable built-in :class:`dict` class. It overrides one method and adds one writable
instance variable. The remaining functionality is the same as for the instance variable. The remaining functionality is the same as for the
:class:`dict` class and is not documented here. :class:`dict` class and is not documented here.
The first argument provides the initial value for the :attr:`default_factory` The first argument provides the initial value for the :attr:`default_factory`
attribute; it defaults to ``None``. All remaining arguments are treated the same attribute; it defaults to ``None``. All remaining arguments are treated the same
as if they were passed to the :class:`dict` constructor, including keyword as if they were passed to the :class:`dict` constructor, including keyword
arguments. arguments.
:class:`defaultdict` objects support the following method in addition to the :class:`defaultdict` objects support the following method in addition to the
standard :class:`dict` operations: standard :class:`dict` operations:
.. method:: __missing__(key) .. method:: __missing__(key)
If the :attr:`default_factory` attribute is ``None``, this raises a If the :attr:`default_factory` attribute is ``None``, this raises a
:exc:`KeyError` exception with the *key* as argument. :exc:`KeyError` exception with the *key* as argument.
If :attr:`default_factory` is not ``None``, it is called without arguments If :attr:`default_factory` is not ``None``, it is called without arguments
to provide a default value for the given *key*, this value is inserted in to provide a default value for the given *key*, this value is inserted in
the dictionary for the *key*, and returned. the dictionary for the *key*, and returned.
If calling :attr:`default_factory` raises an exception this exception is If calling :attr:`default_factory` raises an exception this exception is
propagated unchanged. propagated unchanged.
This method is called by the :meth:`__getitem__` method of the This method is called by the :meth:`__getitem__` method of the
:class:`dict` class when the requested key is not found; whatever it :class:`dict` class when the requested key is not found; whatever it
returns or raises is then returned or raised by :meth:`__getitem__`. returns or raises is then returned or raised by :meth:`__getitem__`.
Note that :meth:`__missing__` is *not* called for any operations besides Note that :meth:`__missing__` is *not* called for any operations besides
:meth:`__getitem__`. This means that :meth:`get` will, like normal :meth:`__getitem__`. This means that :meth:`get` will, like normal
dictionaries, return ``None`` as a default rather than using dictionaries, return ``None`` as a default rather than using
:attr:`default_factory`. :attr:`default_factory`.
:class:`defaultdict` objects support the following instance variable: :class:`defaultdict` objects support the following instance variable:
.. attribute:: default_factory .. attribute:: default_factory
This attribute is used by the :meth:`__missing__` method; it is This attribute is used by the :meth:`__missing__` method; it is
initialized from the first argument to the constructor, if present, or to initialized from the first argument to the constructor, if present, or to
``None``, if absent. ``None``, if absent.
:class:`defaultdict` Examples :class:`defaultdict` Examples
...@@ -618,13 +618,13 @@ stack manipulations such as ``dup``, ``drop``, ``swap``, ``over``, ``pick``, ...@@ -618,13 +618,13 @@ stack manipulations such as ``dup``, ``drop``, ``swap``, ``over``, ``pick``,
Using :class:`list` as the :attr:`default_factory`, it is easy to group a Using :class:`list` as the :attr:`default_factory`, it is easy to group a
sequence of key-value pairs into a dictionary of lists: sequence of key-value pairs into a dictionary of lists:
>>> s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)] >>> s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)]
>>> d = defaultdict(list) >>> d = defaultdict(list)
>>> for k, v in s: >>> for k, v in s:
... d[k].append(v) ... d[k].append(v)
... ...
>>> list(d.items()) >>> list(d.items())
[('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])] [('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])]
When each key is encountered for the first time, it is not already in the When each key is encountered for the first time, it is not already in the
mapping; so an entry is automatically created using the :attr:`default_factory` mapping; so an entry is automatically created using the :attr:`default_factory`
...@@ -634,24 +634,24 @@ again, the look-up proceeds normally (returning the list for that key) and the ...@@ -634,24 +634,24 @@ again, the look-up proceeds normally (returning the list for that key) and the
:meth:`list.append` operation adds another value to the list. This technique is :meth:`list.append` operation adds another value to the list. This technique is
simpler and faster than an equivalent technique using :meth:`dict.setdefault`: simpler and faster than an equivalent technique using :meth:`dict.setdefault`:
>>> d = {} >>> d = {}
>>> for k, v in s: >>> for k, v in s:
... d.setdefault(k, []).append(v) ... d.setdefault(k, []).append(v)
... ...
>>> list(d.items()) >>> list(d.items())
[('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])] [('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])]
Setting the :attr:`default_factory` to :class:`int` makes the Setting the :attr:`default_factory` to :class:`int` makes the
:class:`defaultdict` useful for counting (like a bag or multiset in other :class:`defaultdict` useful for counting (like a bag or multiset in other
languages): languages):
>>> s = 'mississippi' >>> s = 'mississippi'
>>> d = defaultdict(int) >>> d = defaultdict(int)
>>> for k in s: >>> for k in s:
... d[k] += 1 ... d[k] += 1
... ...
>>> list(d.items()) >>> list(d.items())
[('i', 4), ('p', 2), ('s', 4), ('m', 1)] [('i', 4), ('p', 2), ('s', 4), ('m', 1)]
When a letter is first encountered, it is missing from the mapping, so the When a letter is first encountered, it is missing from the mapping, so the
:attr:`default_factory` function calls :func:`int` to supply a default count of :attr:`default_factory` function calls :func:`int` to supply a default count of
...@@ -662,23 +662,23 @@ constant functions. A faster and more flexible way to create constant functions ...@@ -662,23 +662,23 @@ constant functions. A faster and more flexible way to create constant functions
is to use a lambda function which can supply any constant value (not just is to use a lambda function which can supply any constant value (not just
zero): zero):
>>> def constant_factory(value): >>> def constant_factory(value):
... return lambda: value ... return lambda: value
>>> d = defaultdict(constant_factory('<missing>')) >>> d = defaultdict(constant_factory('<missing>'))
>>> d.update(name='John', action='ran') >>> d.update(name='John', action='ran')
>>> '%(name)s %(action)s to %(object)s' % d >>> '%(name)s %(action)s to %(object)s' % d
'John ran to <missing>' 'John ran to <missing>'
Setting the :attr:`default_factory` to :class:`set` makes the Setting the :attr:`default_factory` to :class:`set` makes the
:class:`defaultdict` useful for building a dictionary of sets: :class:`defaultdict` useful for building a dictionary of sets:
>>> s = [('red', 1), ('blue', 2), ('red', 3), ('blue', 4), ('red', 1), ('blue', 4)] >>> s = [('red', 1), ('blue', 2), ('red', 3), ('blue', 4), ('red', 1), ('blue', 4)]
>>> d = defaultdict(set) >>> d = defaultdict(set)
>>> for k, v in s: >>> for k, v in s:
... d[k].add(v) ... d[k].add(v)
... ...
>>> list(d.items()) >>> list(d.items())
[('blue', {2, 4}), ('red', {1, 3})] [('blue', {2, 4}), ('red', {1, 3})]
:func:`namedtuple` Factory Function for Tuples with Named Fields :func:`namedtuple` Factory Function for Tuples with Named Fields
...@@ -690,69 +690,69 @@ they add the ability to access fields by name instead of position index. ...@@ -690,69 +690,69 @@ they add the ability to access fields by name instead of position index.
.. function:: namedtuple(typename, field_names, verbose=False, rename=False) .. function:: namedtuple(typename, field_names, verbose=False, rename=False)
Returns a new tuple subclass named *typename*. The new subclass is used to Returns a new tuple subclass named *typename*. The new subclass is used to
create tuple-like objects that have fields accessible by attribute lookup as create tuple-like objects that have fields accessible by attribute lookup as
well as being indexable and iterable. Instances of the subclass also have a well as being indexable and iterable. Instances of the subclass also have a
helpful docstring (with typename and field_names) and a helpful :meth:`__repr__` helpful docstring (with typename and field_names) and a helpful :meth:`__repr__`
method which lists the tuple contents in a ``name=value`` format. method which lists the tuple contents in a ``name=value`` format.
The *field_names* are a single string with each fieldname separated by whitespace The *field_names* are a single string with each fieldname separated by whitespace
and/or commas, for example ``'x y'`` or ``'x, y'``. Alternatively, *field_names* and/or commas, for example ``'x y'`` or ``'x, y'``. Alternatively, *field_names*
can be a sequence of strings such as ``['x', 'y']``. can be a sequence of strings such as ``['x', 'y']``.
Any valid Python identifier may be used for a fieldname except for names Any valid Python identifier may be used for a fieldname except for names
starting with an underscore. Valid identifiers consist of letters, digits, starting with an underscore. Valid identifiers consist of letters, digits,
and underscores but do not start with a digit or underscore and cannot be and underscores but do not start with a digit or underscore and cannot be
a :mod:`keyword` such as *class*, *for*, *return*, *global*, *pass*, a :mod:`keyword` such as *class*, *for*, *return*, *global*, *pass*,
or *raise*. or *raise*.
If *rename* is true, invalid fieldnames are automatically replaced If *rename* is true, invalid fieldnames are automatically replaced
with positional names. For example, ``['abc', 'def', 'ghi', 'abc']`` is with positional names. For example, ``['abc', 'def', 'ghi', 'abc']`` is
converted to ``['abc', '_1', 'ghi', '_3']``, eliminating the keyword converted to ``['abc', '_1', 'ghi', '_3']``, eliminating the keyword
``def`` and the duplicate fieldname ``abc``. ``def`` and the duplicate fieldname ``abc``.
If *verbose* is true, the class definition is printed after it is If *verbose* is true, the class definition is printed after it is
built. This option is outdated; instead, it is simpler to print the built. This option is outdated; instead, it is simpler to print the
:attr:`_source` attribute. :attr:`_source` attribute.
Named tuple instances do not have per-instance dictionaries, so they are Named tuple instances do not have per-instance dictionaries, so they are
lightweight and require no more memory than regular tuples. lightweight and require no more memory than regular tuples.
.. versionchanged:: 3.1 .. versionchanged:: 3.1
Added support for *rename*. Added support for *rename*.
.. doctest:: .. doctest::
:options: +NORMALIZE_WHITESPACE :options: +NORMALIZE_WHITESPACE
>>> # Basic example >>> # Basic example
>>> Point = namedtuple('Point', ['x', 'y']) >>> Point = namedtuple('Point', ['x', 'y'])
>>> p = Point(11, y=22) # instantiate with positional or keyword arguments >>> p = Point(11, y=22) # instantiate with positional or keyword arguments
>>> p[0] + p[1] # indexable like the plain tuple (11, 22) >>> p[0] + p[1] # indexable like the plain tuple (11, 22)
33 33
>>> x, y = p # unpack like a regular tuple >>> x, y = p # unpack like a regular tuple
>>> x, y >>> x, y
(11, 22) (11, 22)
>>> p.x + p.y # fields also accessible by name >>> p.x + p.y # fields also accessible by name
33 33
>>> p # readable __repr__ with a name=value style >>> p # readable __repr__ with a name=value style
Point(x=11, y=22) Point(x=11, y=22)
Named tuples are especially useful for assigning field names to result tuples returned Named tuples are especially useful for assigning field names to result tuples returned
by the :mod:`csv` or :mod:`sqlite3` modules:: by the :mod:`csv` or :mod:`sqlite3` modules::
EmployeeRecord = namedtuple('EmployeeRecord', 'name, age, title, department, paygrade') EmployeeRecord = namedtuple('EmployeeRecord', 'name, age, title, department, paygrade')
import csv import csv
for emp in map(EmployeeRecord._make, csv.reader(open("employees.csv", "rb"))): for emp in map(EmployeeRecord._make, csv.reader(open("employees.csv", "rb"))):
print(emp.name, emp.title) print(emp.name, emp.title)
import sqlite3 import sqlite3
conn = sqlite3.connect('/companydata') conn = sqlite3.connect('/companydata')
cursor = conn.cursor() cursor = conn.cursor()
cursor.execute('SELECT name, age, title, department, paygrade FROM employees') cursor.execute('SELECT name, age, title, department, paygrade FROM employees')
for emp in map(EmployeeRecord._make, cursor.fetchall()): for emp in map(EmployeeRecord._make, cursor.fetchall()):
print(emp.name, emp.title) print(emp.name, emp.title)
In addition to the methods inherited from tuples, named tuples support In addition to the methods inherited from tuples, named tuples support
three additional methods and two attributes. To prevent conflicts with three additional methods and two attributes. To prevent conflicts with
...@@ -760,62 +760,63 @@ field names, the method and attribute names start with an underscore. ...@@ -760,62 +760,63 @@ field names, the method and attribute names start with an underscore.
.. classmethod:: somenamedtuple._make(iterable) .. classmethod:: somenamedtuple._make(iterable)
Class method that makes a new instance from an existing sequence or iterable. Class method that makes a new instance from an existing sequence or iterable.
.. doctest:: .. doctest::
>>> t = [11, 22] >>> t = [11, 22]
>>> Point._make(t) >>> Point._make(t)
Point(x=11, y=22) Point(x=11, y=22)
.. method:: somenamedtuple._asdict() .. method:: somenamedtuple._asdict()
Return a new :class:`OrderedDict` which maps field names to their corresponding Return a new :class:`OrderedDict` which maps field names to their corresponding
values:: values. Note, this method is no longer needed now that the same effect can
be achieved by using the built-in :func:`vars` function::
>>> p._asdict() >>> vars(p)
OrderedDict([('x', 11), ('y', 22)]) OrderedDict([('x', 11), ('y', 22)])
.. versionchanged:: 3.1 .. versionchanged:: 3.1
Returns an :class:`OrderedDict` instead of a regular :class:`dict`. Returns an :class:`OrderedDict` instead of a regular :class:`dict`.
.. method:: somenamedtuple._replace(kwargs) .. method:: somenamedtuple._replace(kwargs)
Return a new instance of the named tuple replacing specified fields with new Return a new instance of the named tuple replacing specified fields with new
values: values:
:: ::
>>> p = Point(x=11, y=22) >>> p = Point(x=11, y=22)
>>> p._replace(x=33) >>> p._replace(x=33)
Point(x=33, y=22) Point(x=33, y=22)
>>> for partnum, record in inventory.items(): >>> for partnum, record in inventory.items():
... inventory[partnum] = record._replace(price=newprices[partnum], timestamp=time.now()) ... inventory[partnum] = record._replace(price=newprices[partnum], timestamp=time.now())
.. attribute:: somenamedtuple._source .. attribute:: somenamedtuple._source
A string with the pure Python source code used to create the named A string with the pure Python source code used to create the named
tuple class. The source makes the named tuple self-documenting. tuple class. The source makes the named tuple self-documenting.
It can be printed, executed using :func:`exec`, or saved to a file It can be printed, executed using :func:`exec`, or saved to a file
and imported. and imported.
.. versionadded:: 3.3 .. versionadded:: 3.3
.. attribute:: somenamedtuple._fields .. attribute:: somenamedtuple._fields
Tuple of strings listing the field names. Useful for introspection Tuple of strings listing the field names. Useful for introspection
and for creating new named tuple types from existing named tuples. and for creating new named tuple types from existing named tuples.
.. doctest:: .. doctest::
>>> p._fields # view the field names >>> p._fields # view the field names
('x', 'y') ('x', 'y')
>>> Color = namedtuple('Color', 'red green blue') >>> Color = namedtuple('Color', 'red green blue')
>>> Pixel = namedtuple('Pixel', Point._fields + Color._fields) >>> Pixel = namedtuple('Pixel', Point._fields + Color._fields)
>>> Pixel(11, 22, 128, 255, 0) >>> Pixel(11, 22, 128, 255, 0)
Pixel(x=11, y=22, red=128, green=255, blue=0) Pixel(x=11, y=22, red=128, green=255, blue=0)
To retrieve a field whose name is stored in a string, use the :func:`getattr` To retrieve a field whose name is stored in a string, use the :func:`getattr`
function: function:
...@@ -826,24 +827,24 @@ function: ...@@ -826,24 +827,24 @@ function:
To convert a dictionary to a named tuple, use the double-star-operator To convert a dictionary to a named tuple, use the double-star-operator
(as described in :ref:`tut-unpacking-arguments`): (as described in :ref:`tut-unpacking-arguments`):
>>> d = {'x': 11, 'y': 22} >>> d = {'x': 11, 'y': 22}
>>> Point(**d) >>> Point(**d)
Point(x=11, y=22) Point(x=11, y=22)
Since a named tuple is a regular Python class, it is easy to add or change Since a named tuple is a regular Python class, it is easy to add or change
functionality with a subclass. Here is how to add a calculated field and functionality with a subclass. Here is how to add a calculated field and
a fixed-width print format: a fixed-width print format:
>>> class Point(namedtuple('Point', 'x y')): >>> class Point(namedtuple('Point', 'x y')):
__slots__ = () __slots__ = ()
@property @property
def hypot(self): def hypot(self):
return (self.x ** 2 + self.y ** 2) ** 0.5 return (self.x ** 2 + self.y ** 2) ** 0.5
def __str__(self): def __str__(self):
return 'Point: x=%6.3f y=%6.3f hypot=%6.3f' % (self.x, self.y, self.hypot) return 'Point: x=%6.3f y=%6.3f hypot=%6.3f' % (self.x, self.y, self.hypot)
>>> for p in Point(3, 4), Point(14, 5/7): >>> for p in Point(3, 4), Point(14, 5/7):
print(p) print(p)
Point: x= 3.000 y= 4.000 hypot= 5.000 Point: x= 3.000 y= 4.000 hypot= 5.000
Point: x=14.000 y= 0.714 hypot=14.018 Point: x=14.000 y= 0.714 hypot=14.018
...@@ -870,19 +871,19 @@ and more efficient to use a simple class declaration: ...@@ -870,19 +871,19 @@ and more efficient to use a simple class declaration:
>>> Status.open, Status.pending, Status.closed >>> Status.open, Status.pending, Status.closed
(0, 1, 2) (0, 1, 2)
>>> class Status: >>> class Status:
open, pending, closed = range(3) open, pending, closed = range(3)
.. seealso:: .. seealso::
* `Named tuple recipe <http://code.activestate.com/recipes/500261/>`_ * `Named tuple recipe <http://code.activestate.com/recipes/500261/>`_
adapted for Python 2.4. adapted for Python 2.4.
* `Recipe for named tuple abstract base class with a metaclass mix-in * `Recipe for named tuple abstract base class with a metaclass mix-in
<http://code.activestate.com/recipes/577629-namedtupleabc-abstract-base-class-mix-in-for-named/>`_ <http://code.activestate.com/recipes/577629-namedtupleabc-abstract-base-class-mix-in-for-named/>`_
by Jan Kaliszewski. Besides providing an :term:`abstract base class` for by Jan Kaliszewski. Besides providing an :term:`abstract base class` for
named tuples, it also supports an alternate :term:`metaclass`-based named tuples, it also supports an alternate :term:`metaclass`-based
constructor that is convenient for use cases where named tuples are being constructor that is convenient for use cases where named tuples are being
subclassed. subclassed.
:class:`OrderedDict` objects :class:`OrderedDict` objects
...@@ -894,36 +895,36 @@ the items are returned in the order their keys were first added. ...@@ -894,36 +895,36 @@ the items are returned in the order their keys were first added.
.. class:: OrderedDict([items]) .. class:: OrderedDict([items])
Return an instance of a dict subclass, supporting the usual :class:`dict` Return an instance of a dict subclass, supporting the usual :class:`dict`
methods. An *OrderedDict* is a dict that remembers the order that keys methods. An *OrderedDict* is a dict that remembers the order that keys
were first inserted. If a new entry overwrites an existing entry, the were first inserted. If a new entry overwrites an existing entry, the
original insertion position is left unchanged. Deleting an entry and original insertion position is left unchanged. Deleting an entry and
reinserting it will move it to the end. reinserting it will move it to the end.
.. versionadded:: 3.1 .. versionadded:: 3.1
.. method:: popitem(last=True) .. method:: popitem(last=True)
The :meth:`popitem` method for ordered dictionaries returns and removes a The :meth:`popitem` method for ordered dictionaries returns and removes a
(key, value) pair. The pairs are returned in LIFO order if *last* is true (key, value) pair. The pairs are returned in LIFO order if *last* is true
or FIFO order if false. or FIFO order if false.
.. method:: move_to_end(key, last=True) .. method:: move_to_end(key, last=True)
Move an existing *key* to either end of an ordered dictionary. The item Move an existing *key* to either end of an ordered dictionary. The item
is moved to the right end if *last* is true (the default) or to the is moved to the right end if *last* is true (the default) or to the
beginning if *last* is false. Raises :exc:`KeyError` if the *key* does beginning if *last* is false. Raises :exc:`KeyError` if the *key* does
not exist:: not exist::
>>> d = OrderedDict.fromkeys('abcde') >>> d = OrderedDict.fromkeys('abcde')
>>> d.move_to_end('b') >>> d.move_to_end('b')
>>> ''.join(d.keys()) >>> ''.join(d.keys())
'acdeb' 'acdeb'
>>> d.move_to_end('b', last=False) >>> d.move_to_end('b', last=False)
>>> ''.join(d.keys()) >>> ''.join(d.keys())
'bacde' 'bacde'
.. versionadded:: 3.2 .. versionadded:: 3.2
In addition to the usual mapping methods, ordered dictionaries also support In addition to the usual mapping methods, ordered dictionaries also support
reverse iteration using :func:`reversed`. reverse iteration using :func:`reversed`.
...@@ -941,8 +942,8 @@ semantics pass-in keyword arguments using a regular unordered dictionary. ...@@ -941,8 +942,8 @@ semantics pass-in keyword arguments using a regular unordered dictionary.
.. seealso:: .. seealso::
`Equivalent OrderedDict recipe <http://code.activestate.com/recipes/576693/>`_ `Equivalent OrderedDict recipe <http://code.activestate.com/recipes/576693/>`_
that runs on Python 2.4 or later. that runs on Python 2.4 or later.
:class:`OrderedDict` Examples and Recipes :class:`OrderedDict` Examples and Recipes
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...@@ -985,7 +986,7 @@ original insertion position is changed and moved to the end:: ...@@ -985,7 +986,7 @@ original insertion position is changed and moved to the end::
An ordered dictionary can be combined with the :class:`Counter` class An ordered dictionary can be combined with the :class:`Counter` class
so that the counter remembers the order elements are first encountered:: so that the counter remembers the order elements are first encountered::
class OrderedCounter(Counter, OrderedDict): class OrderedCounter(Counter, OrderedDict):
'Counter that remembers the order elements are first encountered' 'Counter that remembers the order elements are first encountered'
def __repr__(self): def __repr__(self):
...@@ -1006,19 +1007,19 @@ attribute. ...@@ -1006,19 +1007,19 @@ attribute.
.. class:: UserDict([initialdata]) .. class:: UserDict([initialdata])
Class that simulates a dictionary. The instance's contents are kept in a Class that simulates a dictionary. The instance's contents are kept in a
regular dictionary, which is accessible via the :attr:`data` attribute of regular dictionary, which is accessible via the :attr:`data` attribute of
:class:`UserDict` instances. If *initialdata* is provided, :attr:`data` is :class:`UserDict` instances. If *initialdata* is provided, :attr:`data` is
initialized with its contents; note that a reference to *initialdata* will not initialized with its contents; note that a reference to *initialdata* will not
be kept, allowing it be used for other purposes. be kept, allowing it be used for other purposes.
In addition to supporting the methods and operations of mappings, In addition to supporting the methods and operations of mappings,
:class:`UserDict` instances provide the following attribute: :class:`UserDict` instances provide the following attribute:
.. attribute:: data .. attribute:: data
A real dictionary used to store the contents of the :class:`UserDict` A real dictionary used to store the contents of the :class:`UserDict`
class. class.
...@@ -1036,19 +1037,19 @@ to work with because the underlying list is accessible as an attribute. ...@@ -1036,19 +1037,19 @@ to work with because the underlying list is accessible as an attribute.
.. class:: UserList([list]) .. class:: UserList([list])
Class that simulates a list. The instance's contents are kept in a regular Class that simulates a list. The instance's contents are kept in a regular
list, which is accessible via the :attr:`data` attribute of :class:`UserList` list, which is accessible via the :attr:`data` attribute of :class:`UserList`
instances. The instance's contents are initially set to a copy of *list*, instances. The instance's contents are initially set to a copy of *list*,
defaulting to the empty list ``[]``. *list* can be any iterable, for defaulting to the empty list ``[]``. *list* can be any iterable, for
example a real Python list or a :class:`UserList` object. example a real Python list or a :class:`UserList` object.
In addition to supporting the methods and operations of mutable sequences, In addition to supporting the methods and operations of mutable sequences,
:class:`UserList` instances provide the following attribute: :class:`UserList` instances provide the following attribute:
.. attribute:: data .. attribute:: data
A real :class:`list` object used to store the contents of the A real :class:`list` object used to store the contents of the
:class:`UserList` class. :class:`UserList` class.
**Subclassing requirements:** Subclasses of :class:`UserList` are expect to **Subclassing requirements:** Subclasses of :class:`UserList` are expect to
offer a constructor which can be called with either no arguments or one offer a constructor which can be called with either no arguments or one
...@@ -1073,10 +1074,10 @@ attribute. ...@@ -1073,10 +1074,10 @@ attribute.
.. class:: UserString([sequence]) .. class:: UserString([sequence])
Class that simulates a string or a Unicode string object. The instance's Class that simulates a string or a Unicode string object. The instance's
content is kept in a regular string object, which is accessible via the content is kept in a regular string object, which is accessible via the
:attr:`data` attribute of :class:`UserString` instances. The instance's :attr:`data` attribute of :class:`UserString` instances. The instance's
contents are initially set to a copy of *sequence*. The *sequence* can contents are initially set to a copy of *sequence*. The *sequence* can
be an instance of :class:`bytes`, :class:`str`, :class:`UserString` (or a 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 subclass) or an arbitrary sequence which can be converted into a string using
the built-in :func:`str` function. the built-in :func:`str` function.
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