skiplistcollections (original) (raw)

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

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

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

Changes

0.0.6

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

0.0.5

Fixed SkipListDict repr
Created SkipListSet

0.0.4

Included start_key and reverse values in views reprs
Improved README

0.0.3

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

0.0.2

Improved README

Copyright

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