Python, as a rule, uses
lowercase_with_underscores for method and function names. The
threading module incorrectly used
mixedCase for many of the names when first added to Python. They later added the
lowercase_with_underscores names as aliases for style consistency with the rest of Python.
In general, use the
lowercase_with_underscores names unless your code needs to run on Python 2.5 or earlier (the fixed names were added in 2.6). That said, the docs note:
Note: Starting with Python 2.6, this module provides PEP 8 compliant aliases and properties to replace the camelCase names that were inspired by Java’s threading API. This updated API is compatible with that of the multiprocessing module. However, no schedule has been set for the deprecation of the camelCase names and they remain fully supported in both Python 2.x and 3.x.