Args and kwargs are great features of Python. There is a measurable (though highly variable) cost of them however:
>>> timeit.timeit(lambda: (lambda a, b: None)(1, b=2))
0.16460260000000204
>>> timeit.timeit(lambda: (lambda *a, **kw: None)(1, b=2))
0.21245309999999762
>>> timeit.timeit(lambda: (lambda *a, **kw: None)(1, b=2)) - timeit.timeit(lambda: (lambda a, b: None)(1, b=2))
0.14699769999992895
Constructing that dict and tuple doesn't happen for free:
>>> timeit.timeit(lambda: ((1,), {'b': 2})) - timeit.timeit(lambda: None)
0.16881599999999253
Specifically, it takes about 1/5,000,000th of a second.
>>> timeit.timeit(lambda: (lambda a, b: None)(1, b=2))
0.16460260000000204
>>> timeit.timeit(lambda: (lambda *a, **kw: None)(1, b=2))
0.21245309999999762
>>> timeit.timeit(lambda: (lambda *a, **kw: None)(1, b=2)) - timeit.timeit(lambda: (lambda a, b: None)(1, b=2))
0.14699769999992895
Constructing that dict and tuple doesn't happen for free:
>>> timeit.timeit(lambda: ((1,), {'b': 2})) - timeit.timeit(lambda: None)
0.16881599999999253
Specifically, it takes about 1/5,000,000th of a second.