Planarity

The planarity repository provides the source code for the planarity Python package. The planarity package was originally developed to provide Python and NetworkX developers with a Python API to access planar graph testing, embedding, drawing, and forbidden subgraph isolation algorithms from the Edge Addition Planarity Suite (EAPS).

The planarity repository has now been transferred to the Github Graph Algorithms Organization. The planarity repository and Python package have been updated with the full set of planarity-related algorithms from EAPS as well as all public methods from its generalized graph library to enable development of a wide range of high-performance graph algorithms and applications.

Example

In [1]: # Example of the complete graph of 5 nodes, K5

In [2]: # K5 is not planar

In [3]: import planarity

In [4]: edgelist = [('a', 'b'), ('a', 'c'), ('a', 'd'), ('a', 'e'),
   ...:             ('b', 'c'),('b', 'd'),('b', 'e'),
   ...:             ('c', 'd'), ('c', 'e'),
   ...:             ('d', 'e')]

In [5]: print(planarity.is_planar(edgelist))
False

In [6]: # remove an edge to make the graph planar

In [7]: edgelist.remove(('a','b'))

In [8]: print(planarity.is_planar(edgelist))
True

In [9]: # make an ascii text drawing

In [10]: print(planarity.ascii(edgelist))

----1----
| | |   |
| | -3--|
| |  ||||
| -2--|||
|  |  |||
---4---||
 |     ||
 ---5----

In [11]: # Shows correspondence between vertex labels and indices

In [12]: print(planarity.mapping(edgelist))
{1: 'd', 2: 'c', 3: 'e', 4: 'a', 5: 'b'}

See here for more examples.

For further details on development setup and installation, please see this wiki page on the planarity repository.

License

Planarity (the 'planarity' Python package; the software) is released under this BSD-3-Clause license.

Copyright (c) 2016-2026, Planarity Developers
John M. Boyer john.boyer.phd@gmail.com
Wanda B. K. Boyer wbkboyer@gmail.com
Aric Hagberg aric.hagberg@gmail.com
All rights reserved.

Planarity includes the Edge Addition Planarity Suite, which is
Copyright (c) 1997-2026, John M. Boyer.
The BSD-3-Clause license for the Edge Additional Planarity Suite included in Planarity appears here.