[Python-Dev] Examples for PEP 572

[David Mertz]

Hmmm... I admit I didn't expect quite this behavior. I'm don't actually
understand why it's doing what it does.

>>> def myfun():
...    print(globals().update({'foo', 43}), foo)
...
>>> myfun()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in myfun
TypeError: cannot convert dictionary update sequence element #0 to a
sequence

That said, this is a silly game either way.  And even though you CAN
(sometimes) bind in an expression pre-572, that's one of those perverse
corners that one shouldn't actually use.

On Wed, Jul 4, 2018 at 9:58 AM Chris Angelico <rosuav at gmail.com> wrote:

> On Wed, Jul 4, 2018 at 11:52 PM, David Mertz <mertz at gnosis.cx> wrote:
> > On Wed, Jul 4, 2018 at 3:02 AM Chris Angelico <rosuav at gmail.com> wrote:
> >>
> >> "Assignment is a statement" -- that's exactly the point under
> discussion.
> >> "del is a statement" -- yes, granted
> >> "function and class declarations are statements" -- class, yes, but
> >> you have "def" and "lambda" as statement and expression equivalents.
> >> "import is a statement" -- but importlib.import_module exists for a
> reason
> >>
> >> I'm going to assume that your term "mutating" there was simply a
> >> miswording, and that you're actually talking about *name binding*,
> >> which hitherto occurs only in statements. Yes, this is true.
> >
> >
> > Nope, not actually:
> >
> >>>> del foo
> >>>> print(globals().update({'foo':42}), foo)
> > None 42
> >
>
> Try it inside a function though.
>
> ChrisA
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