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[John Posner]

>     I have 2 lists
> a = [(4, 1), (7, 3), (3, 2), (2, 4)]
> b = [2, 4, 1, 3]
> 
>     Now, I want to order _a_ (a[1]) based on _b_.
>     i.e. the second element in tuple should be the same as
> b.
>     i.e. Output would be [(3, 2), (2, 4), (4, 1), (7, 3)]
> 
>     I did the same as follows:
> >>> l = len(a) * [None]
> >>> for (k, v) in a:
> ...   for i, e in enumerate(b):
> ...     if e == v:
> ...        l[i] = (k, v)
> 

Essentially, you're sorting a list. The Pythonic approach is to use the sort() function, hiding the details in a "custom comparison function":

def compare_func(first, second):
    b = [2, 4, 1, 3]    
    return cmp(b.index(first[1]), b.index(second[1]))
    
if __name__ == '__main__':
    a = [(4, 1), (7, 3), (3, 2), (2, 4)]
    a.sort(cmp=compare_func)
    print a 

-John