--- /dev/null
+# -*- coding: utf-8 -*-
+
+# An ordered dictionary implementation. OrderedDict entered the
+# Python Standard Library in Python 2.7 and 3.1. See `PEP 372`_ for
+# details. Code_ by Armin Ronacher and the PEP 273 authors.
+#
+# .. _PEP 372: http://www.python.org/dev/peps/pep-0372/
+# .. _Code: http://dev.pocoo.org/hg/sandbox/raw-file/tip/odict.py
+
+"""
+ odict
+ ~~~~~
+
+ This module is an example implementation of an ordered dict for the
+ collections module. It's not written for performance (it actually
+ performs pretty bad) but to show how the API works.
+
+
+ Questions and Answers
+ =====================
+
+ Why would anyone need ordered dicts?
+
+ Dicts in python are unordered which means that the order of items when
+ iterating over dicts is undefined. As a matter of fact it is most of
+ the time useless and differs from implementation to implementation.
+
+ Many developers stumble upon that problem sooner or later when
+ comparing the output of doctests which often does not match the order
+ the developer thought it would.
+
+ Also XML systems such as Genshi have their problems with unordered
+ dicts as the input and output ordering of tag attributes is often
+ mixed up because the ordering is lost when converting the data into
+ a dict. Switching to lists is often not possible because the
+ complexity of a lookup is too high.
+
+ Another very common case is metaprogramming. The default namespace
+ of a class in python is a dict. With Python 3 it becomes possible
+ to replace it with a different object which could be an ordered dict.
+ Django is already doing something similar with a hack that assigns
+ numbers to some descriptors initialized in the class body of a
+ specific subclass to restore the ordering after class creation.
+
+ When porting code from programming languages such as PHP and Ruby
+ where the item-order in a dict is guaranteed it's also a great help
+ to have an equivalent data structure in Python to ease the transition.
+
+ Where are new keys added?
+
+ At the end. This behavior is consistent with Ruby 1.9 Hashmaps
+ and PHP Arrays. It also matches what common ordered dict
+ implementations do currently.
+
+ What happens if an existing key is reassigned?
+
+ The key is *not* moved. This is consitent with existing
+ implementations and can be changed by a subclass very easily::
+
+ class movingodict(odict):
+ def __setitem__(self, key, value):
+ self.pop(key, None)
+ odict.__setitem__(self, key, value)
+
+ Moving keys to the end of a ordered dict on reassignment is not
+ very useful for most applications.
+
+ Does it mean the dict keys are sorted by a sort expression?
+
+ That's not the case. The odict only guarantees that there is an order
+ and that newly inserted keys are inserted at the end of the dict. If
+ you want to sort it you can do so, but newly added keys are again added
+ at the end of the dict.
+
+ I initializes the odict with a dict literal but the keys are not
+ ordered like they should!
+
+ Dict literals in Python generate dict objects and as such the order of
+ their items is not guaranteed. Before they are passed to the odict
+ constructor they are already unordered.
+
+ What happens if keys appear multiple times in the list passed to the
+ constructor?
+
+ The same as for the dict. The latter item overrides the former. This
+ has the side-effect that the position of the first key is used because
+ the key is actually overwritten:
+
+ >>> odict([('a', 1), ('b', 2), ('a', 3)])
+ odict.odict([('a', 3), ('b', 2)])
+
+ This behavor is consistent with existing implementation in Python
+ and the PHP array and the hashmap in Ruby 1.9.
+
+ This odict doesn't scale!
+
+ Yes it doesn't. The delitem operation is O(n). This is file is a
+ mockup of a real odict that could be implemented for collections
+ based on an linked list.
+
+ Why is there no .insert()?
+
+ There are few situations where you really want to insert a key at
+ an specified index. To now make the API too complex the proposed
+ solution for this situation is creating a list of items, manipulating
+ that and converting it back into an odict:
+
+ >>> d = odict([('a', 42), ('b', 23), ('c', 19)])
+ >>> l = d.items()
+ >>> l.insert(1, ('x', 0))
+ >>> odict(l)
+ odict.odict([('a', 42), ('x', 0), ('b', 23), ('c', 19)])
+
+ :copyright: (c) 2008 by Armin Ronacher and PEP 273 authors.
+ :license: modified BSD license.
+"""
+from itertools import izip, imap
+from copy import deepcopy
+
+missing = object()
+
+
+class odict(dict):
+ """
+ Ordered dict example implementation.
+
+ This is the proposed interface for a an ordered dict as proposed on the
+ Python mailinglist (proposal_).
+
+ It's a dict subclass and provides some list functions. The implementation
+ of this class is inspired by the implementation of Babel but incorporates
+ some ideas from the `ordereddict`_ and Django's ordered dict.
+
+ The constructor and `update()` both accept iterables of tuples as well as
+ mappings:
+
+ >>> d = odict([('a', 'b'), ('c', 'd')])
+ >>> d.update({'foo': 'bar'})
+ >>> d
+ odict.odict([('a', 'b'), ('c', 'd'), ('foo', 'bar')])
+
+ Keep in mind that when updating from dict-literals the order is not
+ preserved as these dicts are unsorted!
+
+ You can copy an odict like a dict by using the constructor, `copy.copy`
+ or the `copy` method and make deep copies with `copy.deepcopy`:
+
+ >>> from copy import copy, deepcopy
+ >>> copy(d)
+ odict.odict([('a', 'b'), ('c', 'd'), ('foo', 'bar')])
+ >>> d.copy()
+ odict.odict([('a', 'b'), ('c', 'd'), ('foo', 'bar')])
+ >>> odict(d)
+ odict.odict([('a', 'b'), ('c', 'd'), ('foo', 'bar')])
+ >>> d['spam'] = []
+ >>> d2 = deepcopy(d)
+ >>> d2['spam'].append('eggs')
+ >>> d
+ odict.odict([('a', 'b'), ('c', 'd'), ('foo', 'bar'), ('spam', [])])
+ >>> d2
+ odict.odict([('a', 'b'), ('c', 'd'), ('foo', 'bar'), ('spam', ['eggs'])])
+
+ All iteration methods as well as `keys`, `values` and `items` return
+ the values ordered by the the time the key-value pair is inserted:
+
+ >>> d.keys()
+ ['a', 'c', 'foo', 'spam']
+ >>> d.values()
+ ['b', 'd', 'bar', []]
+ >>> d.items()
+ [('a', 'b'), ('c', 'd'), ('foo', 'bar'), ('spam', [])]
+ >>> list(d.iterkeys())
+ ['a', 'c', 'foo', 'spam']
+ >>> list(d.itervalues())
+ ['b', 'd', 'bar', []]
+ >>> list(d.iteritems())
+ [('a', 'b'), ('c', 'd'), ('foo', 'bar'), ('spam', [])]
+
+ Index based lookup is supported too by `byindex` which returns the
+ key/value pair for an index:
+
+ >>> d.byindex(2)
+ ('foo', 'bar')
+
+ You can reverse the odict as well:
+
+ >>> d.reverse()
+ >>> d
+ odict.odict([('spam', []), ('foo', 'bar'), ('c', 'd'), ('a', 'b')])
+
+ And sort it like a list:
+
+ >>> d.sort(key=lambda x: x[0].lower())
+ >>> d
+ odict.odict([('a', 'b'), ('c', 'd'), ('foo', 'bar'), ('spam', [])])
+
+ .. _proposal: http://thread.gmane.org/gmane.comp.python.devel/95316
+ .. _ordereddict: http://www.xs4all.nl/~anthon/Python/ordereddict/
+ """
+
+ def __init__(self, *args, **kwargs):
+ dict.__init__(self)
+ self._keys = []
+ self.update(*args, **kwargs)
+
+ def __delitem__(self, key):
+ dict.__delitem__(self, key)
+ self._keys.remove(key)
+
+ def __setitem__(self, key, item):
+ if key not in self:
+ self._keys.append(key)
+ dict.__setitem__(self, key, item)
+
+ def __deepcopy__(self, memo=None):
+ if memo is None:
+ memo = {}
+ d = memo.get(id(self), missing)
+ if d is not missing:
+ return d
+ memo[id(self)] = d = self.__class__()
+ dict.__init__(d, deepcopy(self.items(), memo))
+ d._keys = self._keys[:]
+ return d
+
+ def __getstate__(self):
+ return {'items': dict(self), 'keys': self._keys}
+
+ def __setstate__(self, d):
+ self._keys = d['keys']
+ dict.update(d['items'])
+
+ def __reversed__(self):
+ return reversed(self._keys)
+
+ def __eq__(self, other):
+ if isinstance(other, odict):
+ if not dict.__eq__(self, other):
+ return False
+ return self.items() == other.items()
+ return dict.__eq__(self, other)
+
+ def __ne__(self, other):
+ return not self.__eq__(other)
+
+ def __cmp__(self, other):
+ if isinstance(other, odict):
+ return cmp(self.items(), other.items())
+ elif isinstance(other, dict):
+ return dict.__cmp__(self, other)
+ return NotImplemented
+
+ @classmethod
+ def fromkeys(cls, iterable, default=None):
+ return cls((key, default) for key in iterable)
+
+ def clear(self):
+ del self._keys[:]
+ dict.clear(self)
+
+ def copy(self):
+ return self.__class__(self)
+
+ def items(self):
+ return zip(self._keys, self.values())
+
+ def iteritems(self):
+ return izip(self._keys, self.itervalues())
+
+ def keys(self):
+ return self._keys[:]
+
+ def iterkeys(self):
+ return iter(self._keys)
+
+ def pop(self, key, default=missing):
+ if default is missing:
+ return dict.pop(self, key)
+ elif key not in self:
+ return default
+ self._keys.remove(key)
+ return dict.pop(self, key, default)
+
+ def popitem(self, key):
+ self._keys.remove(key)
+ return dict.popitem(key)
+
+ def setdefault(self, key, default=None):
+ if key not in self:
+ self._keys.append(key)
+ dict.setdefault(self, key, default)
+
+ def update(self, *args, **kwargs):
+ sources = []
+ if len(args) == 1:
+ if hasattr(args[0], 'iteritems'):
+ sources.append(args[0].iteritems())
+ else:
+ sources.append(iter(args[0]))
+ elif args:
+ raise TypeError('expected at most one positional argument')
+ if kwargs:
+ sources.append(kwargs.iteritems())
+ for iterable in sources:
+ for key, val in iterable:
+ self[key] = val
+
+ def values(self):
+ return map(self.get, self._keys)
+
+ def itervalues(self):
+ return imap(self.get, self._keys)
+
+ def index(self, item):
+ return self._keys.index(item)
+
+ def byindex(self, item):
+ key = self._keys[item]
+ return (key, dict.__getitem__(self, key))
+
+ def reverse(self):
+ self._keys.reverse()
+
+ def sort(self, *args, **kwargs):
+ self._keys.sort(*args, **kwargs)
+
+ def __repr__(self):
+ return 'odict.odict(%r)' % self.items()
+
+ __copy__ = copy
+ __iter__ = iterkeys
+
+
+if __name__ == '__main__':
+ import doctest
+ doctest.testmod()
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