[Python-Dev] Python3 compiled listcomp can't see local var (original) (raw)

Rob Cliffe rob.cliffe at btinternet.com
Mon Jun 11 18:06:36 EDT 2018

Skip, I think you have misunderstood the  point I was making.  It was not whether the loop variable should leak out of a list comprehension.  Rather, it was whether a local variable should, so to speak, "leak into" a list comprehension.  And the answer is: it depends on whether the code is executed normally, or via exec/eval.  Example:

def Test():       x = 1       print([x+i for i in range(1,3)])              # Prints [2,3]       exec('print([x+i for i in range(1,3)])') # Raises NameError (x) Test()

I (at least at first) found the difference in behaviour surprising.

Regards

Rob Cliffe

On 08/06/2018 19:27, Skip Montanaro wrote:

Is this a bug or a feature? The bug was me being so excited about the new construct (I pushed in someone else's work, can't recall who now, maybe Fredrik Lundh?) that I didn't consider that leaking the loop variable out of the list comprehension was a bad idea. Think of the Py3 behavior as one of those "corrections" to things which were "got wrong" in Python 1 or 2. :-) Skip --- This email has been checked for viruses by AVG. http://www.avg.com

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