On 15 April 2018 at 13:54, Chris Angelico <ros...@gmail.com> wrote: > On Sun, Apr 15, 2018 at 1:08 PM, Nick Coghlan <ncogh...@gmail.com> wrote: >> === Target first, 'from' keyword === >> >> while (value from read_next_item()) is not None: # New >> ... >> >> Pros: >> >> * avoids the syntactic ambiguity of "as" >> * being target first provides an obvious distinction from the "as" keyword >> * typically reads nicely as pseudocode >> * "from" is already associated with a namebinding operation ("from >> module import name") >> >> Cons: >> >> * I'm sure we'll think of some more, but all I have so far is that >> the association with name binding is relatively weak and would need to >> be learned >> > > Cons: Syntactic ambiguity with "raise exc from otherexc", probably not > serious.
Ah, I forgot about that usage. The keyword usage is at least somewhat consistent, in that it's short for: _tmp = exc _exc.__cause__ from otherexc raise exc However, someone writing "raise (ExcType from otherexc)" could be confusing, since it would end up re-raising "otherexc" instead of wrapping it in a new ExcType instance. If "otherexc" was also an ExcType instance, that would be a *really* subtle bug to try and catch, so this would likely need the same kind of special casing as was proposed for "as" (i.e. prohibiting the top level parentheses). I also agree with Nathan that if you hadn't encountered from expressions before, it would be reasonable to assume they were semantically comparable to "target = next(expr)" rather than just "target = expr". Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Python-ideas mailing list Pythonfirstname.lastname@example.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/