I know python and want to contribute on OpenSource projects that features python. Anyone can help me where to contribute and how.
I already googled it and find github and code.google as a good place to contribute but how to start it I don't know.
Suggest how to get started.
Not sure if this is an appropriate question for SO - you might get voted down. But ...
Whenever I have seen this question, the answer is almost always:

find a project you like / you're interested in
find something in that project that you feel you can fix / enhance (have a look through their bug tracker)
fork the project (github makes this easy)
make the change, find out what is appropriate for that project (documentation, unit tests, ...)
submit the change back to the project (github has "request pull")

Good luck!
how to contribute on open source project featuring python