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A MutableSet that remembers its order, so that every entry has an index.

Project description

An OrderedSet is a custom MutableSet that remembers its order, so that every entry has an index that can be looked up.

Based on a recipe originally posted to ActiveState Recipes by Raymond Hettiger, and released under the MIT license:

http://code.activestate.com/recipes/576694-orderedset/

Rob Speer’s changes are as follows:

  • changed the content from a doubly-linked list to a regular Python list. Seriously, who wants O(1) deletes but O(N) lookups by index?
  • add() returns the index of the added item
  • index() just returns the index of an item
  • added a __getstate__ and __setstate__ so it can be pickled
  • added __getitem__
  • __getitem__ and index() can be passed lists or arrays, looking up all the elements in them to perform NumPy-like “fancy indexing”

Tested on Python 2.6, 2.7, 3.3, 3.4, 3.5, PyPy, and PyPy3.

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