diff options
Diffstat (limited to 'Lib')
| -rw-r--r-- | Lib/collections.py | 38 |
1 files changed, 25 insertions, 13 deletions
diff --git a/Lib/collections.py b/Lib/collections.py index f1b62c7..bb5991c 100644 --- a/Lib/collections.py +++ b/Lib/collections.py @@ -18,6 +18,18 @@ from itertools import repeat as _repeat, chain as _chain, starmap as _starmap ################################################################################ class OrderedDict(dict, MutableMapping): + 'Dictionary that remembers insertion order' + # The inherited dict maps keys to values. + # The internal self.__map dictionary maps keys to links in a doubly linked list. + # The doubly linked list starts and ends with a sentinel element. + # The sentinel element never gets deleted. It simplifies the algorithm. + # Setting a new item cause a new link to append to the doubly linked list. + # Deleting an item uses self.__map to find the link, which is then removed. + # Iteration follows the linked list in order. + # Reverse iteration follows the links backwards. + # The inherited dict provides __getitem__, __len__, __contains__, and get. + # The remaining methods are order-aware. + # Big-Oh running times for all methods is the same as for regular dictionaries. def __init__(self, *args, **kwds): if len(args) > 1: @@ -49,24 +61,17 @@ class OrderedDict(dict, MutableMapping): def __iter__(self): end = self.__end - curr = end[2] + curr = end[2] # start at first link while curr is not end: - yield curr[0] - curr = curr[2] + yield curr[0] # yield KEY for each link + curr = curr[2] # goto next link def __reversed__(self): end = self.__end - curr = end[1] + curr = end[1] # start at last link while curr is not end: - yield curr[0] - curr = curr[1] - - def popitem(self, last=True): - if not self: - raise KeyError('dictionary is empty') - key = next(reversed(self)) if last else next(iter(self)) - value = self.pop(key) - return key, value + yield curr[0] # yield KEY for each link + curr = curr[1] # goto prev link def __reduce__(self): items = [[k, self[k]] for k in self] @@ -85,6 +90,13 @@ class OrderedDict(dict, MutableMapping): values = MutableMapping.values items = MutableMapping.items + def popitem(self, last=True): + if not self: + raise KeyError('dictionary is empty') + key = next(reversed(self)) if last else next(iter(self)) + value = self.pop(key) + return key, value + def __repr__(self): if not self: return '%s()' % (self.__class__.__name__,) |