[Python-Dev] listcomps vs. for loops
mwh at python.net
Tue Oct 21 10:45:00 EDT 2003
Jp Calderone <exarkun at intarweb.us> writes:
> On Tue, Oct 21, 2003 at 12:41:00PM +0100, Michael Hudson wrote:
>> Guido van Rossum <guido at python.org> writes:
>> > I don't recall what I said then. Did I say it was a feature that
>> > L = [x for x in R]
>> > print x
>> > would print the last item of R?
>> A problem with such code irrespective of anything else is that it
>> fails when R is empty.
> Not when x is properly initialized.
> Anyway, this is no different from the
> problem of:
> for x in R:
> print x
Well, yes. I still think it's dubious code.
> In any case, are there plans to also have the compiler emit warnings about
> potential reliance on this feature?
I would hope that we wouldn't make changes without emitting such a
warning. I'm not sure how hard it would be to implement, tho'.
(It would be /nice/ to implement a warning whenever there's a
possibility of the UnboundLocalError exception, but that *definitely*
requires control flow analysis and that is *definitely* a heap of
work, unless the ast-branch gets some attention).
We did requirements and task analysis, iterative design, and user
testing. You'd almost think programming languages were an interface
between people and computers. -- Steven Pemberton
(one of the designers of Python's direct ancestor ABC)
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