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An Ordered Set implementation in Cython.

Project Description

An Ordered Set implementation in Cython. Based on Raymond Hettinger’s OrderedSet recipe.


>>> from orderedset import OrderedSet
>>> oset = OrderedSet([1, 2, 3])
>>> oset
OrderedSet([1, 2, 3])
>>> oset | [5, 4, 3, 2, 1]
OrderedSet([1, 2, 3, 5, 4])


  • Works like a regular set, but remembers insertion order;
  • Is approximately 5 times faster than the pure Python implementation overall (and 5 times slower than set);
  • Compatible with Python 2.6 through 3.6.;
  • Supports the full set interface;
  • Supports some list methods, like index and __getitem__.
  • Supports set methods against iterables.


2.0.1 - 2018-03-20

  • bugfix: Fix isdisjoint to return True when the sets are disjoint
  • build: Include 3.6 when testing
  • dist: Include test files in sdist
  • docs: Make the Readme a bit prettier

2.0 - 2016-02-02

  • breaking change: All comparisons, other than eq, against other ordered sets are now performed unordered; i.e., they are treated as regular sets.
  • isorderedsubset and isorderedsuperset have been added to perform ordered comparisons against other sequences. Using these methods with unordered collections wield yield arbitrary (and depending on Python implementation, unstable) results.

1.2 - 2015-09-29

  • bugfix: Set operations only worked with iterables if the OrderedSet was on the left-hand side. They now work both ways.
  • bugfix: The order of an intersection was the right-hand side’s order. It is now fixed to be the left-hand side’s order.

1.1.2 - 2014-10-02

  • Make comparisons work with sets and lists, and not crash when compared with None.

1.1.1 - 2014-08-24

  • Add pickle/copy support to OrderedSet

1.1 - 2014-06-04

  • Make OrderedSets handle slicing in __getitem__().

1.0.2 - 2014-05-14

  • Add proper attribution and licenses.

1.0.1 - 2014-05-13

  • Don’t require Cython to build an sdist.

1.0 - 2014-05-11

  • First implementation.

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