On 14 October 2016 at 10:48, Paul Moore <p.f.mo...@gmail.com> wrote: > On 14 October 2016 at 07:54, Greg Ewing <greg.ew...@canterbury.ac.nz> wrote: >>> I think it's probably time for someone to >>> describe the precise syntax (as BNF, like the syntax in the Python >>> docs at >>> https://docs.python.org/3.6/reference/expressions.html#displays-for-lists-sets-and-dictionaries >> >> >> Replace >> >> comprehension ::= expression comp_for >> >> with >> >> comprehension ::= (expression | "*" expression) comp_for >> >>> and semantics (as an explanation of how to >>> rewrite any syntactically valid display as a loop). >> >> >> The expansion of the "*" case is the same as currently except >> that 'append' is replaced by 'extend' in a list comprehension, >> 'yield' is replaced by 'yield from' in a generator >> comprehension. [...] > So now I understand what's being proposed, which is good. I don't > (personally) find it very intuitive, although I'm completely capable > of using the rules given to establish what it means. In practical > terms, I'd be unlikely to use or recommend it - not because of > anything specific about the proposal, just because it's "confusing". I > would say the same about [(x, *y, z) for ...].
Thinking some more about this, is it not true that [ *expression for var in iterable ] is the same as [ x for var in iterable for x in expression ] ? If so, then this proposal adds no new expressiveness, merely a certain amount of "compactness". Which isn't necessarily a bad thing, but it's clearly controversial whether the compact version is more readable / "intuitive" in this case. Given the lack of any clear improvement, I'd be inclined to think that "explicit is better than implicit" applies here, and reject the new proposal. Paul. _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
