[HelloNurse]

I'd emphasize that for each tasks that's likely to be a performance bottleneck there are, usually, existing high performance extensions: someone has had the same needs before you.

If there are performance issues, rewriting part of a Python application in C is much less likely than refactoring it, without using other languages, to use an existing high performance library.

Application-specific Python extensions are usually intended to allow scripting of the application, with little concern for Python performance (which is the same as doing the same thing without scripting).

New foreign language Python extensions are usually found in new Python libraries, to make existing proven C or C++ libraries available to Python applications or to improve on existing Python libraries.