On Fri, Nov 24, 2017 at 1:21 AM, Paul Moore <p.f.mo...@gmail.com> wrote: > On 23 November 2017 at 13:04, Ivan Levkivskyi <levkivs...@gmail.com> wrote: >> Let us forget for a moment about other problems and focus on this one: list >> comprehension is currently not equivalent to a for-loop. >> There are two options: >> - Fix this, i.e. make comprehension equivalent to a for-loop even in edge >> cases (Serhiy seems ready to do this) >> - Prohibit all cases when they are not equivalent >> >> I still prefer option one. But I see your point, option two is also an >> acceptable fix. >> Note that there were not so many situations when some code became >> SyntaxError later. >> I don't see why this particular case qualifies for such a radical measure as >> an exception to syntactic rules, >> instead of just fixing it (sorry Nick :-) > > My main concern is that comprehension is not equivalent to a for loop > for a specific reason - the scope issue. Has anyone looked back at the > original discussions to confirm *why* a function was used? > > My recollection: > >>>> i = 1 >>>> a = [i for i in (1,2,3)] >>>> print(i) > 1 > > Serihy's approach (and your described expansion) would have print(i) > return NameError. > > So - do we actually have a proposal to avoid the implied function that > *doesn't* break this example? I'm pretty sure this was a real-life > issue at the time we switched to the current implementation.
A while back I had a POC patch that made "with EXPR as NAME:" create a new subscope with NAME in it, such that the variable actually disappeared at the end of the 'with' block. Should I try to track that down and adapt the technique to comprehensions? The subscope shadows names exactly the way a nested function does, but it's all within the same function. ChrisA _______________________________________________ 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
