Geometry2D | helper classes for 2D geometric calculations | 3D Animation library

The reason to not change method signatures in subclasses is so that you can take an instance of class Foo and call methods of Foo on that instance without needing to know the exact subclass to know what arguments to pass.

That doesn't apply to __init__ (except in multiple inheritance, which is one of the reasons it's so easy to get multiple inheritance wrong). You always know what __init__ you're going to invoke (except in multiple inheritance), so changing the signature of __init__ in a subclass is fine (except in multiple inheritance).