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. -- Craig
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