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

You get an error because webdriver is a module inside the selenium module, and you can't access modules without an explicit import statement.

If you take a look at help(selenium), you'll see there are two modules and one non-module contained inside.

PACKAGE CONTENTS
    common (package)
    selenium
    webdriver (package)

And it behaves according to what I described above:

>>> selenium.common # doesn't work
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'common'
>>> from selenium import common # works
>>> selenium.selenium # works
<class 'selenium.selenium.selenium'>
>>> selenium.webdriver # doesn't work
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'webdriver'
>>> from selenium import webdriver # works
>>>