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Mon Jan 12 12:31:14 EST 2004 · https://mail.python.org/pipermail/python-dev/2004-January/041956.html

> 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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[Python-Dev] [872326] generator expression implementation