I guess this is intended not documented:

http://docs.python.org/dev/py3k/library/profile.html#extensions-deriving-better-profilers

Here it said:
"The Profile class of both modules, profile and cProfile, were written so that derived classes could be developed to extend the profiler. The details are not described here, as doing this successfully requires an expert understanding of how the Profile class works internally. Study the source code of the module carefully if you want to pursue this."

These sentences guide reader to read the source code.