[Python-ideas] Conditional Assignment in If Statement

[Michael duPont]

It was not my intention to declare those to be similar, just as a
furthering train of thought. I agree that using "as" is a much more
Pythonic syntax. I'm sure there was (and will be) some discussion as to
whether it should operate like "if foo:" or "if foo is not None:". I'll
look a bit further into the archives than I did to find previous
discussions. For now, I'm a fan of:

if get_foo() as foo:
    bar(foo)

to replace the "if foo:" version:

foo = get_foo()
if foo:
    bar(foo)
del foo

On Mon, Oct 17, 2016 at 6:18 PM Chris Angelico <rosuav at gmail.com> wrote:

> On Tue, Oct 18, 2016 at 9:11 AM, Michael duPont <michael at mdupont.com>
> wrote:
> > What does everyone think about:
> >
> > if foo = get_foo():
> >     bar(foo)
> >
> > as a means to replace:
> >
> > foo = get_foo()
> > if not foo:
> >     bar(foo)
> > del foo
> >
> > Might there be some better syntax or a different keyword? I constantly
> run into this sort of use case.
>
> I'm pretty sure that syntax is never going to fly, for a variety of
> reasons (to see most of them, just read up a C style guide). But this
> syntax has been proposed now and then, analogously with the 'with'
> statement:
>
> if get_foo() as foo:
>     bar(foo)
>
> Be careful of your definitions, though. You've said these as equivalent:
>
> if foo = get_foo():
>     bar(foo)
>
> foo = get_foo()
> if foo is not None:
>     bar(foo)
>
> foo = get_foo()
> if not foo:
>     bar(foo)
> del foo
>
> There are three quite different conditions here. Your last two are
> roughly opposites of each other; but also, most people would expect
> "if foo = get_foo()" to be the same condition as "if get_foo()", which
> is not the same as "if get_foo() is not None". The semantics most
> likely to be accepted would be for "if get_foo() as foo:" to use the
> standard boolification rules of Python (and then make 'foo' available
> in both 'if' and 'else' blocks). Would you support that? If so, check
> out some of the previous threads on the subject - this is far from the
> first time it's been discussed, and most likely won't be the last.
>
> ChrisA
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