[Python-Dev] [872326] generator expression implementation
Guido van Rossum
guido at python.org
Mon Jan 12 12:31:14 EST 2004
> Sorry to bring this out again, I didn't find a reference about the following
> issue in generator expressions:
>
> (for x in expr)
>
> When should 'expr' be evaluated? A priori, one would expect it to be
> evaluated immediately, but it is not what the suggested implementation does:
>
> def __gen():
> for x in expr:
> yield x
> __gen()
>
> This only computes expr when the first element of the generator is needed (so
> it may even never be computed). Is it done purposefully? It may also be
> surprising to see the anonymous generator in tracebacks if an exception is
> raised within expr.
Looks like a bug to me; I'd like to hear arguments to the contrary.
--Guido van Rossum (home page: http://www.python.org/~guido/)
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