Big time WTF with generators - bug?
jstroud at mbi.ucla.edu
Wed Feb 13 09:57:15 CET 2008
Paul Rubin wrote:
> James Stroud <jstroud at mbi.ucla.edu> writes:
>> I defined a little debugging function called iterprint:
>> def iterprint(thing): ...
>> for x in thing:
> of course this mutates the thing that is being printed. Try using
> itertools.tee to fork a copy of the iterator and print from that.
> I didn't look at the rest of your code enough to spot any errors
> but take note of the warnings in the groupby documentation about
> pitfalls with using the results some number of times other than
> exactly once.
I can see I didn't explain so well. This one must be a bug if my code
looks good to you. Here is a summary:
- If I iterprint inside the loop, iterprint looks correct.
- If I iterprint outside the loop, my generator gets consumed and I am
only left with the last item, so my iterprint prints only one item
outside the loop.
Conclusion: something consumes my generator going from inside the loop
Please note that I am not talking about the yielded values, or the
for-loop that creates them. I left them there to show my intent with the
function. The iterprint function is there to show that the generator
gets consumed just moving from inside the loop to outside.
I know this one is easy to dismiss to my consuming the generator with
the iterprint, as this would be a common mistake.
UCLA-DOE Institute for Genomics and Proteomics
Los Angeles, CA 90095
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