For Python, I really like reading Kenneth Reitz' code. For example the Requests library is pretty good reading [0]. When reading code, I like to have the documentation handy as well [1].

The Django project is also good reading. [2], [3]

[0] - Requests code: https://github.com/kennethreitz/requests

[1] - Requests documentation: http://docs.python-requests.org/en/master/

[2] - Django code: https://github.com/django/django

[3] - Django documentation: https://docs.djangoproject.com/en/1.10/