On 20 April 2018 at 21:25, Christoph Groth <christ...@grothesque.org> wrote: > Steven Turnbull wrote: >> >> Christoph Groth writes: >> >>> Wouldn't it be a pity not to liberate assignments from their boring >>> statement existence? >> >> >> Maybe not. While it would be nice to solve the loop-and-a-half >> "problem" and the loop variable initialization "problem" (not everyone >> agrees these are even problems, especially now that we have >> comprehensions and generator expressions), as a matter of taste I like >> the fact that this particular class of side effects is given weighty >> statement syntax rather than more lightweight expression syntax. > > > I think that this is the crucial point. If it is indeed a design > principle of Python that expressions should not have the side-effect of > assigning names, than the whole discussion of PEP 572 could have been > stopped early on. I didn't have this impression since core devs > participated constructively in the discussion.
There were a couple of factors at play there. Firstly, python-ideas and python-dev play different roles in the process, with python-ideas focused on "Help PEP authors put forward the most compelling proposal possible", and then python-dev providing the far more stringent filter of "Do we sincerely believe the long term improvements in language learnability and code maintainability arising from this change will outweigh the inevitable near term costs?" (python-ideas does consider the latter question as well, but we're more willing to spend time on ideas that only reach the level "Maybe? Depending on your point of view?"). Secondly, the original PEP proposed sublocal scopes *precisely* to help preserve that property by limiting the impact of any name binding side effects to a single statement (albeit an arbtirarily long nested suite in the case of compound statements). My own enthusiasm for the idea largely waned after folks successfully campaigned for "we'd prefer side effects to introducing a new kind of scope" (and while I'm definitely sympathetic to the "Python's name lookup scoping rules are already excessively complicated" point of view, I also think that if "=" and ":=" both target the same kind of scope, there isn't enough new expressiveness introduced by the latter to justify the syntactic complexity of adding it). Cheers, Nick. P.S. While I'm not planning to work on it myself anytime soon, I think the sublocal scoping semantics proposed in earlier versions of PEP 572 would provide a *much* better developer experience for PEP 3150's "given" clause (which is currently deferred indefinitely, as even I don't particularly like the current incarnation of that proposal). -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ 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
