This is much clearer.  What you got is a limitation of getfullargspec relative to signature (see the links).  In this case, you want follow_wrapped=True, to get the specific signature of the wrapped function instead of the generic signature of the wrapper*. With the patch, the tip in 3.6 and 3.7 is '(n, k)'.  So yes, this is one of the changes consequent on the switch.  

>>> str(inspect.signature(f,follow_wrapped=False))
'(*args, **kw)'