Pycallgraph is a python package for creating a visual representation of the call graph of your application. Its very useful for profiling to detect performance bottlenecks or to find out what the heck actually happens if you execute the program.
I wanted to use it for that exact reasons in a tool that is still stuck on Python 2.6 and had to find out that Pycallgraph is incompatible with that ancient version and requires at least Python 2.7.
Luckily I was able to change that, so for everyone encountering the same issue I uploaded the 2.6-compatible version: https://bitbucket.org/cb109/pycallgraph26
Please see the usage instructions and a list of modifications in the readme of the repository.