Graphing retweets with Python and GraphViz

On the microblogging site twitter, a blog post is called an update, or informally, a tweet. When someone copies a tweet and posts it to their twitter feed, it’s called a retweet. Sometimes opinions are retweeted by those who share them, other times it’s information, and other times it’s silly memes. This evening, a local friend of mine on twitter started a meme by saying “tweet.” and asking for a retweet. One person who retweeted it got his message retweeted.

I know I’m not the first person to graph retweets, but being curious as to what this particular graph would look like, I decided to do a graph in Python as a programming exercise. I did it using a GraphViz library. The code is here:

import pydot

graph = pydot.Dot('rt', graph_type='digraph')
tweeps = ('tysoncrosbie',
           ('phxreguy',
             ('sbowerman',
               ('phxwebguy', 'leaky_tiki'),
               'refriedchicken')),
           'vhgill',
           'Yartibise')

def add_edge(source, dest):
  graph.add_edge(pydot.Edge(source, dest))

def first_flat(tree):
  if isinstance(tree, tuple):
    return first_flat(tree[0])
  else:
    return tree

def find_edges(tree):
  if isinstance(tree, tuple):
    source = tree[0]
    for dest in tree[1:]:
      add_edge(source, first_flat(dest))
      find_edges(dest)

find_edges(tweeps)
graph.write_png('rt_graph.png')

The code takes a nested list structure (a tree) and produces edges from it, which can be graphed by GraphViz. It uses pydot, a GraphViz library for Python. Here is the resulting image:

Observations:

• Python doesn’t have a built-in list flattening function. This was irritating. Ruby’s is Array#flatten. It would have been so much nicer to have been able to grab the first element of a flattened list rather than write the first_flat function or copy/paste a list-flattening function from the Internet.
• pydot is really simple to use. I liked how it could produce a png file. I was planning just to have it create a dot file and then use GraphViz to create a png, but when I saw the write_png function I decided to just use that.
• GraphViz has reasonable defaults. It produced a nice-looking graph on the first try. I think that’s a big part of why GraphViz is as popular as it is.

I was hoping to have a little more to show for tomorrow’s Python Interest Group meeting, but this will have to do!