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a[0]=[1, 3, 5, 7, 9]
a[1]=[10, 8, 6, 4, 2]

a=[1, 10, 3, 8, 5, 6, 7, 4, 9, 2]

a = range(1, 11)
a=odds, evens = reduce(lambda (a, b), x: x % 2 and (a + [x], b) or (a, b + [x]), a, ([], []))

>>> import itertools
>>> 
>>> a = [1, 3, 5, 7, 9]
>>> b = [10, 8, 6, 4, 2]
>>> 
>>> c = list(itertools.chain.from_iterable(zip(a, b)))
>>> c
[1, 10, 3, 8, 5, 6, 7, 4, 9, 2]
>>>