marc added the comment: I think the problem was a combination of two issues. First, the warning in 16.17.2.2 is a bit hidden. Kind of squeezed in between CDLL, etc and PyDLL. In contrast, 16.17.2.4 does a much better job, because it restates the fact that the GIL is released at each and every item. I think this is much better, because chances are high that you actually read the entry completely. In contrast, in case you are in a hurry you might miss the warning in 16.17.2.2 I think the second problem was that back then I was not aware of the fact that you need the GIL to call the Python/C API. That was a bit stupid indeed. But as a Python beginner it was just not obvious. Maybe the Introduction of the Python/C API needs some work, too. No GIL mentioned at https://docs.python.org/3/c-api/intro.html. Furthermore, the examples at https://docs.python.org/3/extending/extending.html also do not talk about the GIL. ---------- nosy: +marc@bruenink.de _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue18017> _______________________________________