GarlicSim blog

25th February 2011

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Nastiest Python list comprehension ever

I just came up with the nastiest Python list comprehension ever.

Here it is in all its glory:

def mystery(n):
    a = list(range(n))
    return [[i for a[::i] in [a[::i][::-1]]][0] for
             i in a[2:] if a[i] == i] 

I apologize in advance to anyone who will try to understand what this function does and how it works. Hint: It returns a bunch of numbers which have a certain mathematical property.

Actually, its results are not perfect: It throws in a few false positives. I tried to fix it to remove the false positives; I can easily write code that will filter the false positives away, but I want any extra code to live up to the unidiomatism level of the list comprehension itself. That’s not an easy task :)

Does anyone have a suggestion on how to do it?