Why does importing a python module not import nested modules?

Question

If I do this:

import lxml 

in python, lxml.html is not imported. For instance, I cannot call the lxml.html.parse() function. Why is this so?

Answer 1

Importing a module or package in Python is a conceptually simple operation:

1. Find the .py file corresponding to the import. This involves the Python path and some other machinery, but will result in a specific .py file being found.

2. For every directory level in the import (import foo.bar.baz has two levels), find the corresponding __init__.py file, and execute it. Executing it simply means running all the top-level statements in the file.

3. Finally, the .py file itself (foo/bar/baz.py in this case) is executed, meaning all the top-level statements are executed. All the globals created as a result of that execution are bundled into a module object, and that module object is the result of the import.

If none of those steps imported sub-packages, then those sub-packages aren't available. If they did import sub-packages, then they are available. Package authors can do as they wish.