Is there a module cache in python?

Question

When I do:

import os
os.system('pip install nose')
os.system('pip uninstall nose')
import nose

I get an error saying no nose, which is alright.

But when I do this:

import os
os.system('pip install nose')
import nose
del nose
os.system('pip uninstall nose')
import nose

it works! But when I go to the python packages directory, I cannot find nose. Is there some sort of cache for python modules?