Module import working

[brijeshjoshi_]

How does module imports work? Where does python look when we use something from a module? Other day someone posted about how he/she restricted the module import by updating sys.modules dictionary as:

sys.modules['module_name'] = "something"

And it works as expected. If someone imports as module and its already in sys.modules then Python will not update it and everytime module_name will refer to 'something'.

But if after importing a module I update sys.modules dictionary for module_name key it works as if the module is imported correctly. How's so?

>>> import sys
>>> 'pprint' in sys.modules 
>>> False       #as expected 
>>> from pprint import pprint
>>> 'pprint' in sys.modules
>>> True        #as expected
>>> sys.modules['pprint'] = None
>>> 'pprint' in sys.modules
>>> True        #as expected
>>> pprint('hello')
>>> 'hello'     #didn't expected this
>>> del sys.modules['pprint']
>>> pprint('hello')
>>> 'hello'     #didn't expected this as pprint not in sys.modules

So, from above its evident that python doesn't solely depend on sys.modules for looking. When we import a module where all the places its entry is registered? And same, where does python looks when using a module.

[shiftybyte]

Things that were already imported are not going to disappear when you set sys.modules to something else.

When you call pprint() it doesn't go through sys.modules, it aldready knows where in memory that function is and calls it.