There is a sad need for standardization of graphs in Python. The topic has come up numerous times on various mail lists, news groups, forums, etc. There is even a wiki page dedicated to the discussion of the topic on python.org. Ach, when will the madness end?
As far as I can tell, Guido van Rossum essentially solved this issue 10 years ago when he published his paper on Python Patterns - Implementing Graphs. The graph representation is a simple dict and he provided a few functions for demonstration purposes. In 2004, UC Irvine professor David Eppstein started making public his Python graph-theoretic efforts (with a functional programming approach). Both of these represent a direct approach that appeals to my aesthetic sense.
Now, after years of tracking the lack of progress made in standardizing graph representations in Python, I've recently had strong need of them. I did some checking around, and found projects that potentially met my needs. Sadly, none of them had the simplicity of Guido's original implementation (and therefore, anticipated speed benefits).
I was looking for graph implementations with no cruft, no external dependencies, no afterthoughts. I need something that balances runtime performance with a usable API, preferably created using PEP-8 (or similar) coding style.
Here's what I found, with some notes that I used to make a decision for my own needs:
- PADS - David Eppstein's work; functional programming style; very strong math; leaves the implementation of the graph up to the developer-user
- altgraph - too many utility and special-purpose methods for my taste; uses a custom graph object
- python-graph - a new implementation; uses its own objects; seems to take the "framework" approach to graph implementation
- graph - requires the use of custom vertex and edge objects
- NetworkX - fairly complete; lots of redundant code; covers more than just a graph implementation (I only include it here because it seems to be fairly highly used)
In keeping with this motivation, I've started a new project on Launchpad and named it simple-graph. My initial efforts will be aimed at implementing a dict-based graph per Guido's paper, with the possible inclusion of some of David's functions (updated to operate on a dict object). I will then spend some time taking inspiration from the best of what the other graph libraries have to offer while keeping things simple.
As I stated on the web panel at PyCon 2007, diversity is a good thing; it gives us a rich gene pool from which a full and healthy process of natural selection may occur. Let's hope that the efforts of so many Python programmers eventually lead to the inclusion of a graph object in the Python standard library.