Is this kind of behavior actually desirable?

It causes parameter to just "silently get dropped" and users may expect them to have an effect....

I guess I think you should decide on the common signature you want to support.

Does it include **kwargs??

Anyway, we hit this because we subclassed you guys and our signature was:

class Foo(FileLock):
     def __init__(self, *args, new_param=None, **kwargs):
         super().__init__(*args, **kwargs)

and the timeout parameter just got dropped.

In either case, we are just going to stop subclassing, but signature rewriting should really not be used for this kind of convenience stuff.