Peter Hansen wrote:
Steven Bethard wrote:
Diez B. Roggisch wrote:
zip(*[(1,4),(2,5),(3,6)])
While this is also the approach I would use, it is worth noting that Guido thinks of this as an abuse of the argument passing machinery:
http://mail.python.org/pipermail/python-dev/2003-July/037346.html
I'm not sure that's the same thread I already read where he dissed zip like that, but what I'm wondering is what is the alternative? Is there an equally elegant approach that doesn't "abuse" the argument passing machinery?
I know I found it in another thread before. I think he's said it a few times.
Personally, I wish that, if we're not to use zip like this, that Python would provide a builtin 'unzip' to do the corresponding thing.
I never really got the impression that Guido was particularly *strongly* opposed to this use of the extended call syntax. Merely that he was concerned that it would break down if the relevant list turned out to be large (that is, the abuse is using *args with a list when the list may turn out to be large, not a problem specifically with using the star syntax with zip()).
Maybe he's been more explicit somewhere, and I just never saw it.
Anyway, his concern seems justified, as my understanding is that func(*iterable) is roughly equivalent to func(*tuple(iterable)), which can be rather expensive when the iterable is a long list of tuples.
So zip(*zip(*iterable)) is actually zip(*tuple(zip(*tuple(iterable)))). That's potentially an awful lot of data copying for an identity operation :)
Anyway, I think it does make a decent case for an itertools.iunzip or some such beast.
Cheers, Nick.
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Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia
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