Python modules with submodules and functions

A folder with .py files and a __init__.py is called a package. One of those files containing classes and functions is a module. Folder nesting can give you subpackages.

So for example if I had the following structure:

  mypackage
     __init__.py
     module_a.py
     module_b.py
        mysubpackage
             __init__.py
             module_c.py
             module_d.py

I could import mypackage.module_a or mypackage.mysubpackage.module_c and so on.

You could also add functions to mypackage (like the numpy functions you mentioned) by placing that code in the __init__.py. Though this is usually considered to be ugly.

If you look at numpy’s __init__.py you will see a lot of code in there – a lot of this is defining these top-level classes and functions. The __init__.py code is the first thing executed when the package is loaded.