[GVRV]

Ah, you're absolutely correct!

  In [4]: class Test:
     ...:     def test(self, a, b, c=5):
     ...:         return a + b + c
     ...:

  In [5]: inspect.signature(Test.test).parameters
  Out[5]:
  mappingproxy({'self': <Parameter "self">,
              'a': <Parameter "a">,
              'b': <Parameter "b">,
              'c': <Parameter "c=5">})

Then, any idea how you would address the GP's original point? How should "self" be detected if it can be called something else?