[Python-Dev] Python3 compiled listcomp can't see local var - bug or feature?

Rob Cliffe rob.cliffe at btinternet.com
Tue Jun 12 04:38:47 EDT 2018

Ah yes, I see what you mean:

class Test():
        x = 1
        print (x)                         # Prints 1
        print([x+i for i in range(1,3)])  # NameError (x)

Anyway, I  apologise for posting to Python-Dev on was a known issue, and 
turned out to be more me asking for help with development with Python, 
rather than development of Python.  (My original use case was a 
scripting language that could contain embedded Python code).  Thanks to 
Nick for his original answer.

Rob Cliffe

On 11/06/2018 23:31, Eric Fahlgren wrote:
> On Mon, Jun 11, 2018 at 3:10 PM Rob Cliffe via Python-Dev 
> <python-dev at python.org <mailto:python-dev at python.org>> wrote:
>     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.
> ​Change 'def' to 'class' and run it again.  You'll be even more 
> surprised.​
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