On 26 March 2018 at 14:34, Guido van Rossum firstname.lastname@example.org wrote:
Not so fast. There's a perfectly reasonable alternative to sublocal scopes -- just let it assign to a local variable in the containing scope. That's the same as what Python does for for-loop variables. Note that for comprehensions it still happens to do the right thing (assuming we interpret the comprehension's private local scope to be the containing scope).
I finally remembered one of the original reasons that allowing embedded assignment to target regular locals bothered me: it makes named subexpressions public members of the API if you use them at class or module scope. (I sent an off-list email to Chris about that yesterday, so the next update to the PEP is going to take it into account).
Similarly, if you use a named subexpression in a generator or coroutine and it gets placed in the regular locals() namespace, then you've now made that reference live for as long as the generator or coroutine does, even if you never need it again.
By contrast, the sublocals idea strives to keep the *lifecycle* impact of naming a subexpression as negligible as possible - while a named subexpression might live a little longer than it used to as an anonymous subexpression (or substantially longer in the case of compound statement headers), it still wouldn't survive past the end of the statement where it appeared.