On Thu, Jun 28, 2018 at 11:29 AM, Ivan Pozdeev via Python-Dev <python-dev at python.org> wrote: > On 28.06.2018 2:44, Greg Ewing wrote: >> >> Ivan Pozdeev via Python-Dev wrote: >>> >>> for me, the primary use case for an assignment expression is to be able >>> to "catch" a value into a variable in places where I can't put an assignment >>> statement in, like the infamous `if re.match() is not None'. >> >> >> This seems to be one of only about two uses for assignment >> expressions that gets regularly brought up. The other is >> the loop-and-a-half, which is already adequately addressed >> by iterators. >> >> So maybe instead of introducing an out-of-control sledgehammer >> in the form of ":=", we could think about addressing this >> particular case. >> >> Like maybe adding an "as" clause to if-statements: >> >> if pattern.match(s) as m: >> do_something_with(m) >> > > I've skimmed for the origins of "as" (which I remember seeing maybe even > before Py3 was a thing) and found this excellent analysis of modern > languages which is too a part of the PEP 572 discussion: > https://mail.python.org/pipermail/python-ideas/2018-May/050920.html > > It basically concludes that most recently-created languages do not have > assignment expressions; they rather allow assignment statement(s?) before > the tested expression in block statements (only if/while is mentioned. `for' > is not applicable because its exit condition in Python is always the > iterable's exhaustion, there's nothing in it that could be used as a > variable). > Now read this response. https://mail.python.org/pipermail/python-ideas/2018-May/050938.html ChrisA
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