Why does the AttributeError occur

Question

When I import the following:

import scipy # happens with several other modules, too. I took scipy as an example now...

matrix = scipy.sparse.coo_matrix(some_params)

Why does it produce the following error:

AttributeError: 'module' object has no attribute 'sparse'

Answer 1

This happens because the scipy module doesn't have any attribute named sparse. That attribute only gets defined when you import scipy.sparse.

Submodules don't automatically get imported when you just import scipy; you need to import them explicitly. The same holds for most packages, although a package can choose to import its own submodules if it wants to.