Comment by pansa2
Yeah, it was added to tick the box for people who ask "does Python have pattern matching?"
If you look at the feature in detail, and especially how it clashes with the rest of the language, it's awful. For example:
Yeah, it was added to tick the box for people who ask "does Python have pattern matching?"
If you look at the feature in detail, and especially how it clashes with the rest of the language, it's awful. For example:
This isn't about general substitutability though, just about naming constants. If you have `case 404:` and you add a named constant `NOT_FOUND = 404`, you can't change the code to `case NOT_FOUND:` because that completely changes its semantics.
Given that one of the fundamental rules of programming is "don't use magic numbers, prefer named constants", that's terrible language design.
To be fair, "The Substitution Principle" (more commonly known as "equational reasoning" in this context) has never been valid in any languages that aren't... Haskell, and maybe Ada? Any expression that can trigger side effects is an unsafe substitution. (The reason such substitutions are safe in Haskell and Ada is that those languages prevent expressions from triggering side effects in the first place.)