On Sun, 29 Jan 2017 at 16:39 Craig Rodrigues <rodr...@freebsd.org> wrote:
> On Thu, Jan 26, 2017 at 4:09 AM, Ivan Levkivskyi <levkivs...@gmail.com> > wrote: > > > > Concerning list/set/dict comprehensions, I am much more in favor of making > comprehensions simply equivalent to for-loops (more or less like you > proposed using yield from). The only reason to introduce auxiliary function > scope was to prevent the loop variables from leaking outside comprehensions. > Formally, this is indeed backward incompatible, but I doubt many people > depend on the current counter-intuitive behavior. > > Concerning generator expressions, probably it is indeed better to simply > prohibit yield inside them. > > > Thank you to everyone who responded to my post and provided excellent > analysis. > > For Python, I don't know what the best way to proceed is: > > OPTION 1 > ======== > > Make a SyntaxError: [(yield 1) for x in range(10)] > and update the documentation to explain that this is an invalid construct. > > This would have certainly helped me identify the source of the problem as > I tried porting buildbot 0.9 to Python 3. > > However, while not very common, there is Python 2.x code that uses that. > I found these cases in the buildbot code which I changed so as to work on > Python 2 and 3: > > https://github.com/buildbot/buildbot/pull/2661 > https://github.com/buildbot/buildbot/pull/2673 > > > OPTION 2 > ========= > Make this return a list on Python 3, like in Python 2: [ > (yield 1) for x in range(10)] > > As pointed out by others on the this mailing list, there are some > problems associated with that. I don't know if there are many Python 2 > codebases out there > with this construct, but it would be nice to have one less Python 2 -> 3 > porting gotcha. > > > I'm OK with either approach. Leaving things the way they are in Python 3 > is no good, IMHO. > My vote is it be a SyntaxError since you're not getting what you expect from the syntax.
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