This paper analyzes the different GC algorithms and behaviours for CPython and PyPy, and also gives a brief overview of different approaches like GC-as-a-Service. This work has been carried out in the course Seminar on Garbage Collection in January 2012 at the University of Technology in Vienna.
Download the paper here: python_gc_final.pdf (2012-01-22)
For any questions and errata, feel free to contact me.