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

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.​ <http://www.avg.com/email-signature?utmmedium=email&utmsource=link&utmcampaign=sig-email&utmcontent=emailclient> Virus-free. www.avg.com <http://www.avg.com/email-signature?utmmedium=email&utmsource=link&utmcampaign=sig-email&utmcontent=emailclient> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20180612/26307041/attachment.html>

More information about the Python-Dev mailing list