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Add method to OrderedDict for repositioning keys to the ends.

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Raymond Hettinger 2010-09-06 21:26:09 +00:00
parent 7b2a7710ef
commit f45abc97bf
5 changed files with 51 additions and 8 deletions
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23
Lib/collections.py
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@ -173,18 +173,29 @@ class OrderedDict(dict, MutableMapping):
def __del__(self):
self.clear() # eliminate cyclical references
def _renew(self, key, PREV=0, NEXT=1):
'Fast version of self[key]=self.pop(key). Private method for internal use.'
def move_to_end(self, key, last=True, PREV=0, NEXT=1):
'''Move an existing element to the end (or beginning if last==False).
Raises KeyError if the element does not exist.
When last=True, acts like a fast version of self[key]=self.pop(key).
'''
link = self.__map[key]
link_prev = link[PREV]
link_next = link[NEXT]
link_prev[NEXT] = link_next
link_next[PREV] = link_prev
root = self.__root
last = root[PREV]
link[PREV] = last
link[NEXT] = root
last[NEXT] = root[PREV] = link
if last:
last = root[PREV]
link[PREV] = last
link[NEXT] = root
last[NEXT] = root[PREV] = link
else:
first = root[NEXT]
link[PREV] = root
link[NEXT] = first
root[NEXT] = first[PREV] = link
################################################################################