Comment by Spivak
3 days ago
Also this is pretty much in line for the rest of Python leaving variables around.
for x in [1]:
pass
print(x) # => 1
The match statement presented is equivalent to an assignment, you do have to know that, but then it's just regular Python.
Being in line with the bad original design decision is another bad design decision, python developers should have a courage to admit these instances to benefit from better decisions in new peps. They didn't do it with pattern matching and now the language has another inferior implementation of a feature that, if implemented correctly, should have had clear block scopes, defined as expressions (as opposed to statements), and disallowed type-diverging branches. Java has designed it right, by the way, despite having a differently behaving switch statement in the language already.
> Being in line with the bad original design decision is another bad design decision
I disagree. Consistently going with the "bad" choice (in this case, leaking the variable to the outer scope) is better inconsistently swinging between 2 ways of doing things. Least astonishment!
"We've made this mistake before so for consistency we need to repeat it" is such a bad idea. Ideally you want a way to go back and fix things you got wrong, but, even if you can't do that (which is itself a defect and you should figure out how you can improve) you should improve as you move forward.
C++ has struggled with this, so that paper authors sometimes plead with the committee not to make their proposal needlessly worse in the name of "consistency" with existing bad features. This famously failed for std::span, which thus managed to be not only a real world footgun in a language which already has plenty of footguns but also a PR footgun - because for "consistency" the committee removed the safety from the safety feature and I believe in C++ 26 they will repair this so it's just pointless rather than actively worse...
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