This is a nice catch of a subtle bug and a nice fix.  I verified that replacing 'self' with '*args' does not simply shift the problem from 'self' to 'args'.

>>> class C:
	def test(*args, **kwargs):
		print(args, kwargs )
	
>>> c = C()
>>> c.test(1, args=2, kwargs=3, self=4)
(<__main__.C object at 0x00000000035FE128>, 1) {'args': 2, 'kwargs': 3, 'self': 4}

While the * and ** names are, like parameter names, local names given in the signature header, they are not counted as parameter names in the code object .co_argcount or .co_kwonlyargcount attributes that are used along with co_varnames in the name-argument matching process.