On 28 March 2018 at 00:52, Ethan Furman <et...@stoneleaf.us> wrote: > On 03/25/2018 09:46 AM, Ethan Furman wrote: >> >> On 03/24/2018 09:24 PM, Nick Coghlan wrote: >> >>> No, the fact that the expression defining the outermost iterable gets >>> evaluated in the outer scope is behaviour that's >>> explicitly tested for in the regression test suite. >>> >>> The language reference spells out that this is intentional for generator >>> expressions, where it has the added benefit of >>> reporting errors in the outermost iterable expression at the point where >>> the genexp is defined, rather than at the point >>> where it gets iterated over: >>> https://docs.python.org/3/reference/expressions.html#generator-expressions >>> >>> Independently of the pragmatic "getting them to work sensibly at class >>> scope" motivation, comprehensions inherit those >>> semantics by way of the intended semantic equivalence between "[x for x >>> in sequence]" and "list(x for x in sequence)". >> >> >> Thank you (everyone!) for your patience. >> >> Using the latest example from Angelico and myself: >> >> --> d = 9 >> ... def func(_iter): >> ... ... body of comprehension >> --> func((d as e)) >> >> The sticking point is the `func((d as e))`, which to my mind should happen >> inside the comprehension, but needs to happen >> outside -- and the reason it has to happen outside is so that the >> interpretor can verify that `d` actually exists; >> however, I think we can have both: >> >> --> def func(_iter): >> ... ... >> ... e = d >> ... ... >> --> d >> --> func() >> >> This way, the assignment does not leak, but the referenced name is still >> looked up and verified to exist outside the >> function call. >> >> I don't know how easy/difficult that would be to implement. At this point >> a simple confirmation that I understand and >> that in theory the above would solve both issues is what I'm looking for. >> Or, of course, the reasons why the above >> would not, in theory, work. > > > Any insights here? I would rather not say the same things in another thread > if we can resolve this question here and be done with it. :)
Just what Chris said earlier: the expression defining the outermost iterable can be arbitrarily complex, and what you're suggesting would only be feasible for a top-level name binding, not for nested ones. Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
