[Python-ideas] PEP 572: Statement-Local Name Bindings

[Ethan Furman]

On 03/02/2018 11:11 PM, Nick Coghlan wrote:
> On 3 March 2018 at 03:51, Ethan Furman wrote:

>> Ah, right.  Since the PEP primarily covers comprehensions, but then went on to discuss multi-line statements, I had
>> forgotten the comprehension part.  The answer is easy:  assignment expressions in comprehensions stay inside
>> comprehensions, just like other inner comprehension variables already do (function sub-scope, after all).  Thank you
>> for pointing that out.
>
> That wasn't the point I was try to make: my attempted point was that I see allowing an expression like "print((f() as
> x), x^2, x^3)" to overwrite the regular function local "x" as being just as unacceptable as "data = [x^2 for x in
> sequence]" overwriting it, and we already decided that the latter was sufficiently undesirable that we were willing to
> break backwards compatibility in order to change it.

I think I explained myself poorly.  I'm agreeing with you, and pointing out that the (var as expr) syntax /inside/ a 
comprehension would stay inside a comprehension, i.e. not leak out to locals(), just like your "x" above.

--
~Ethan~