>>>def f1(a, b, c=0, *args, **kw):

...     print('a =', a, 'b =', b, 'c =', c, 'args =', args, 'kw =', kw)

>>>def f2(a, b, c=0, *, d, **kw):

...     print('a =', a, 'b =', b, 'c =', c, 'd =', d, 'kw =', kw)

>>> f1(1, 2)

a = 1 b = 2 c = 0 args = () kw = {}

>>> f1(1, 2, c=3)

a = 1 b = 2 c = 3 args = () kw = {}

>>> f1(1, 2, 3, 'a', 'b')

a = 1 b = 2 c = 3 args = ('a', 'b') kw = {}

>>> f1(1, 2, 3, 'a', 'b', x=99)

a = 1 b = 2 c = 3 args = ('a', 'b') kw = {'x': 99}

>>> f2(1, 2, d=99, ext=None)

a = 1 b = 2 c = 0 d = 99 kw = {'ext': None}