Reason for low Pylint ratings of Python standard library code

A friend told me about Pylint and just out of curiosity, I ran it against some of the standard library modules. To my surprise, the ratings were low. Here are a few runs:

os.py
Your code has been rated at 3.55/10 

random.py
Your code has been rated at 4.74/10

I ran it on some more modules and the found the rating to be ~ 6 - 7.

I was wondering the reason behind this? Is Pylint broken or there are more factors to the rating than I am aware of? I am asking this question particularly cause I am new to Python and was depending on Pylint to help me improve my coding style :)