We dropped support for Python 3.3, but some of the docs still refer to it, or "Python 3 before Python 3.4".

https://api.mongodb.com/python/current/examples/authentication.html
https://api.mongodb.com/python/current/installation.html#dependencies (the other optional packages section)
https://github.com/mongodb/mongo-python-driver/blob/3.6.0/README.rst (the same section)