Background: I'm new to Python. I just embedded Python into a multi-threaded application, and extended Python by callbacks as well. During this process I realised that Python is not internally as beautiful as externally. It is not thread safe. This surprised me, because Python is a quite young programming language. I started thinking how to fix this, how to make Python thread safe. Currently Python does not support multiprocessor machines or hyperthreading processors. It is only a matter of time when this has to be fixed, better soon than later. How to make C-api thread safe: It's quite simple, in fact. Thread should first call