Endorsement of list comprehensions

[Alex Martelli]

Skip Montanaro wrote:

> 
>     def qsort2(lst):
>         if len(lst) == 0:
>             return []
>         else:
>             x = lst[0]
>             return (qsort2([i for i in lst[1:] if i<x]) +
>                     [x] +
>                     qsort2([i for i in lst[1:] if i>=x])
> 
> I know this will probably sound odd, but for me, the first time I saw the
> list comprehension expression of quicksort was the first time it was
> immediately apparent to me how quicksort worked.

Actually I prefer the version in recipe 2.11 of the (printed) Cookbook:

def qsort(L):
    if len(L) <= 1: return L
    return qsort([ lt for lt in L[1:] if lt <  L[0] ]) + L[:1] + \
           qsort([ ge for ge in L[1:] if ge >= L[0] ])

but, of course, it IS much of a muchness.  I do agree that this (in
Python just as in the Haskell it was stolen from) is a little gem:-).


Alex