Expert Python Programming - Third Edition

Functions and methods

Functions and methods should be in lowercase with underscores. This rule was not always true in the old standard library modules. Python 3 did a lot of reorganization of the standard library, so most of the functions and methods have a consistent letter case. Still, for some modules such as threading, you can access the old function names that used mixedCase (for example, currentThread). This was left to allow easier backward compatibility, but if you don't need to run your code in older versions of Python, then you should avoid using these old names.

This way of writing methods was common before the lowercase norm became the standard, and some frameworks, such as Zope and Twisted, are also still using mixedCase for ...