On 03/24/2018 09:24 PM, Nick Coghlan wrote:
No, the fact that the expression defining the outermost iterable gets evaluated
in the outer scope is behaviour that's
explicitly tested for in the regression test suite.
The language reference spells out that this is intentional for generator
expressions, where it has the added benefit of
reporting errors in the outermost iterable expression at the point where the
genexp is defined, rather than at the point
where it gets iterated over:
https://docs.python.org/3/reference/expressions.html#generator-expressions
Independently of the pragmatic "getting them to work sensibly at class scope"
motivation, comprehensions inherit those
semantics by way of the intended semantic equivalence between "[x for x in sequence]" and
"list(x for x in sequence)".
Thank you (everyone!) for your patience.
Using the latest example from Angelico and myself:
--> d = 9
... def func(_iter):
... ... body of comprehension
--> func((d as e))
The sticking point is the `func((d as e))`, which to my mind should happen inside the comprehension, but needs to happen
outside -- and the reason it has to happen outside is so that the interpretor can verify that `d` actually exists;
however, I think we can have both:
--> def func(_iter):
... ...
... e = d
... ...
--> d
--> func()
This way, the assignment does not leak, but the referenced name is still looked up and verified to exist outside the
function call.
I don't know how easy/difficult that would be to implement. At this point a simple confirmation that I understand and
that in theory the above would solve both issues is what I'm looking for. Or, of course, the reasons why the above
would not, in theory, work.
--
~Ethan~
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