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Improve iteration speed by only proxying back links.

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The forward links are hard references.
The sentinel element is also a weakref proxy
(to break a forward cylce wrapping around the sentinel).
This commit is contained in:
Raymond Hettinger 2010-09-14 19:40:15 +00:00
parent 328ec7455f
commit f7328d026b
1 changed files with 9 additions and 6 deletions
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15
Lib/collections.py
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@ -32,6 +32,7 @@ class OrderedDict(dict, MutableMapping):
# The internal self.__map dictionary maps keys to links in a doubly linked list.
# The circular doubly linked list starts and ends with a sentinel element.
# The sentinel element never gets deleted (this simplifies the algorithm).
# The sentinel is stored in self.__hardroot with a weakref proxy in self.__root.
# The prev/next links are weakref proxies (to prevent circular references).
# Individual links are kept alive by the hard reference in self.__map.
# Those hard references disappear when a key is deleted from an OrderedDict.
@ -47,7 +48,8 @@ class OrderedDict(dict, MutableMapping):
try:
self.__root
except AttributeError:
self.__root = root = _Link() # sentinel node for the doubly linked list
self.__hardroot = _Link()
self.__root = root = _proxy(self.__hardroot)
root.prev = root.next = root
self.__map = {}
self.update(*args, **kwds)
@ -62,8 +64,9 @@ class OrderedDict(dict, MutableMapping):
root = self.__root
last = root.prev
link.prev, link.next, link.key = last, root, key
last.next = root.prev = proxy(link)
dict.__setitem__(self, key, value)
last.next = link
root.prev = proxy(link)
dict_setitem(self, key, value)
def __delitem__(self, key, dict_delitem=dict.__delitem__):
'od.__delitem__(y) <==> del od[y]'
@ -97,10 +100,10 @@ class OrderedDict(dict, MutableMapping):
def __reduce__(self):
'Return state information for pickling'
items = [[k, self[k]] for k in self]
tmp = self.__map, self.__root
del self.__map, self.__root
tmp = self.__map, self.__root, self.__hardroot
del self.__map, self.__root, self.__hardroot
inst_dict = vars(self).copy()
self.__map, self.__root = tmp
self.__map, self.__root, self.__hardroot = tmp
if inst_dict:
return (self.__class__, (items,), inst_dict)
return self.__class__, (items,)