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Python inports collect the locals in the "module script" and store them in a module object, which is then made available to the module that ran `import`. That module object is cached, so reimporting the module another time will not run the code again.

`source` is much more primitive.

Python imports are much more principled than sourcing bash though. They are executed in a new namespace, and subsequent imports reference that namespace directly instead of re-evaluating the code.

C extensions don't significantly change matters because the module is still constructed by procedural C code.

It’s definitely a feature! Just one that’s often not understood. If you include a file in a C program, that codes just sitting there until you call it (more or less, yada yada #define, etc.). If you import a Python module, it executes the code in it. That code is typically a set of statements that defines functions and classes, but it could be anything.