[Python-ideas] PEP 572 version 2: Statement-Local Name Bindings

[Ethan Furman]

On 03/24/2018 08:51 PM, Chris Angelico wrote:
> On Sun, Mar 25, 2018 at 2:48 PM, Ethan Furman wrote:
>> On 03/24/2018 01:35 AM, Nick Coghlan wrote:
>>
>>> In comprehensions and generator expressions, we'd need to explain why
>>> inline assignments in the outermost iterator
>>> expression leak but those in filter expressions, inner iterator
>>> expressions, and result expressions don't.
>>
>> I don't understand -- could you give an example?
>
> Let's suppose we have assignment expressions. I'm going to use "(expr
> as name)" syntax for this example.
>
> a = [(1 as b) for c in (d as e) if (2 as f)]
>
> Which of these six names is local to the comprehension and which can
> leak? Due to the requirements of class scope, 'd' must be looked up in
> the outer scope. That means that its corresponding 'as e' must also
> land in the outer scope. [...]

Why?

d = 9
def func():
   e = d

d is looked up outside of func, but e is still local to func.

--
~Ethan~