skiplistcollections is a Python module containing skip list based sorted collections. skiplistcollections is written in Python and works with:

• CPython 2.6+, 3.2+
• PyPy 1.9+

Project page on GitHub: https://github.com/jstasiak/skiplistcollections

Project page on PyPI: https://pypi.python.org/pypi/skiplistcollections

SkipListDict is container providing dict-like interface and implemented using skip list. It's permanently sorted by key.

• Iterating the container (starting with any key, supports reverse ordering) is O(n)
• Getting, setting and deleting arbitrary key is O(log n) on average, O(n) in worst case (degenerated skip list)

See http://pythonsweetness.tumblr.com/post/45227295342/fast-pypy-compatible-ordered-map-in-89-lines-of-python for details.

>>> from skiplistcollections import SkipListDict
>>> things = SkipListDict(capacity=16)
>>> len(things)
0
>>> things['x'] = 1
>>> things.setdefault('x', 'DEFAULT')
1
>>> 'x' in things
True
>>> len(things)
1
>>> things['g'] = 2
>>> things['z'] = 3
>>> tuple(things.keys())
('g', 'x', 'z')
>>> tuple(things.values())
(2, 1, 3)
>>> tuple(things.items())
(('g', 2), ('x', 1), ('z', 3))
>>> tuple(things.items(start_key='x'))
(('x', 1), ('z', 3))
>>> tuple(things.items(start_key='x', reverse=True))
(('x', 1), ('g', 2))
>>> del things['z']
>>> things.update({'a': 'A', 'b': 'B'})
>>> len(things)
4
>>> things
SkipListDict({'a': 'A', 'b': 'B', 'g': 2, 'x': 1}, capacity=16)

As you can see, SkipListDict follows Python dict interface quite closely. In fact it inherits MutableMapping Abstract Base Class.

There are differences of course:

• You need to set the maximum dict size when you create it
• Initializing using another mapping is not supported yet
• You can't use None as a key
• items, keys, and values are views and accept start_key and reverse parameters

SkipListSet is set implementation using skip list. It's permanently sorted by key.

• Iterating the container is O(n)
• Adding, removing and checking if a key exist in the containe is O(log n) on average, O(n) in worst case (degenerated skip list)

>>> from skiplistcollections import SkipListSet
>>> things = SkipListSet(capacity=16)
>>> len(things)
0
>>> things.add(3)
>>> len(things)
1
>>> things.add(1)
>>> things.add(4)
>>> things
SkipListSet((1, 3, 4), capacity=16)
>>> tuple(things)
(1, 3, 4)
>>> things.remove(2)
Traceback (most recent call last):
KeyError: 2

• Fixed bug with SkipListDict yielding too many items if start_key was not found (GitHub issue #1)

• Fixed SkipListDict repr
• Created SkipListSet

• Included start_key and reverse values in views reprs
• Improved README

• items(), values(), keys() return views now

• Improved README

Original version - Copyright (C) 2013 David Wilson

Copyright (C) 2013 Jakub Stasiak

This source code is licensed under MIT license, see LICENSE file for details.