https://docs.python.org/2/library/pickle.html#object.__getinitargs__ states:

"If it is desirable that the __init__() method be called on unpickling, an old-style class can define a method __getinitargs__(), which should return a tuple containing the arguments to be passed to the class constructor (__init__() for example)."

However, there is no mention that it only accepts positional arguments.

This is a Python 2-only change and the documentation file is located at Doc/library/pickle.rst in 2.7 branch.