different ways to creating two lists from one

[Fredrik Lundh]

Todd MacCulloch wrote:

> But suppose generating s0 is expensive and/or s0 is big. In otherwords I'd
> like to go over only once and I don't want to keep it around any longer than
> I have to.
>
> I could do something like:
>
> for a, b in [(x + x, x * x) for x in s0]:
>      s1.append(a)
>      s2.append(b)

ouch.

> Is there a better / cleaner way that I'm missing?

    for x in s0:
        s1.append(x + x)
        s2.append(x * x)
    del s0

(memorywise, that's no better than your first alternative.
it's a better than your second alternative, though...)

if s0 contains large and ugly things, you could do something
like this:

    for i, x in enumerate(s0):
        s1.append(x + x)
        s2.append(x * x)
        s0[i] = None

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