Why does an import not always import nested packages?

Question

Why the first code doesn't work while the second does?

First code:

import selenium

driver = selenium.webdriver.Firefox()

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

Second code:

from selenium import webdriver

driver = webdriver.Firefox()

Answer 1

Nested packages are not automatically loaded; not until you import selenium.webdriver is it available as an attribute. Importing just selenium is not enough.

Do this:

import selenium.webdriver

driver = selenium.webdriver.Firefox()

Sometimes the package itself will import a nested package in the __init__.py package initializer; os imports os.path, so os.path is immediately available even if you import just os.