I'm not sure why they removed the ability to destructure sequences in args. It bugs me sometimes as well. There's probably a long discussion about the rationale in some PEP and an even longer email thread.
PEP 3113 -- Removal of Tuple Parameter Unpacking:
def add((a, (b, stack))):
return a + b, stack
def uncons(((head, tail), stack)):
return tail, (head, stack)
In [1]: def foo(a, (b, c)):
...: pass
File "<ipython-input-1-8f113877c7ef>", line 1
def foo(a, (b, c)):
^
SyntaxError: invalid syntax