On 25 June 2018 at 13:24, Nick Coghlan <ncogh...@gmail.com> wrote: > On 25 June 2018 at 22:17, Nick Coghlan <ncogh...@gmail.com> wrote: >> FWIW, the most cryptic parent local scoping related exception I've >> been able to devise so far still exhibits PEP 572's desired "Omitting >> the comprehension scope entirely would give you the same name lookup >> behaviour" semantics: >> >> >>> def outer(x=1): >> ... def middle(): >> ... return [x := x + i for i in range(10)] >> ... return middle() >> ... >> >>> outer() >> Traceback (most recent call last): >> ... >> NameError: free variable 'x' referenced before assignment in enclosing >> scope >> >> It isn't the parent local scoping, or even the assignment expression, >> that's at fault there, since you'd get exactly the same exception for: >> >> def outer(x=1): >> def middle(): >> x = x +1 >> return x >> return middle() > > Oops, I didn't mean to say "exactly the same exception" here, as the > whole reason I'd settled on this example as the most cryptic one I'd > found so far was the fact that the doubly nested version *doesn't* > give you the same exception as the singly nested version: the version > without the comprehension throws UnboundLocalError instead.
At the level of "what my intuition says" the result is the same in both cases - "it throws an exception". I have no intuition on *which* exception would be raised and would experiment (or look up the details) if I cared. > However, the resolution is the same either way: either 'x' has to be > declared as 'nonlocal x' in 'middle', or else it has to be passed in > to 'middle' as a parameter. Once someone told me that's what I needed, it's sufficiently obvious that I'm fine with that. If no-one was able to tell me what to do, I'd simply rewrite the code to be less obfuscated :-) I've probably explained my intuition enough here. If we debate any further I'll just end up knowing what's going on, destroying my value as an "uninformed user" :-) Paul _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
