Re:Go: Redefining For Loop Variable Semantics
by int_19h on Thursday October 13, 2022 @07:57PM
(#33198031)
You're right, but that means that sequence comprehension also leaks the variable, so it's even worse than I thought.
Side note: I think that commenters above didn't quite understand what I meant by "leaking", because there's more than one scope boundary here. Roughly speaking, any comprehension or loop can be desugared into something that looks like a C-style for-loop:
Scope 1 is outside relative to the loop. Scope 2 is specific to the loop but shared by all its iterations. Scope 3 is specific to one loop iteration. The "leaking" I referred to above is from scope 3 to scope 2. I think other commenters took it to mean leaking from scope 2 to scope 1 - i.e. the ability to use the variable outside of the comprehension; that is, indeed, something that changed between Python 2 and 3.
Side note: I think that commenters above didn't quite understand what I meant by "leaking", because there's more than one scope boundary here. Roughly speaking, any comprehension or loop can be desugared into something that looks like a C-style for-loop:
Scope 1 is outside relative to the loop. Scope 2 is specific to the loop but shared by all its iterations. Scope 3 is specific to one loop iteration. The "leaking" I referred to above is from scope 3 to scope 2. I think other commenters took it to mean leaking from scope 2 to scope 1 - i.e. the ability to use the variable outside of the comprehension; that is, indeed, something that changed between Python 2 and 3.