4 ms·
Is it still the case that these two pieces of code have different behaviour? match status: case 404: return "Not found" not_found
by pansa2 6y ago
Is it still the case that these two pieces of code have different behaviour?
match status:
case 404:
return "Not found"
not_found = 404
match status:
case not_found:
return "Not found"
IIRC in an earlier proposal, the former would check for equality (`status == 404`) and the latter would perform an assignment (`not_found = status`).
- bilboa 6y agoYes, the variable names in the case patterns are treated like variables on the left hand side of an assignment statement. Whatever value they may have had before is irrelevant. A pattern which consists solely of a variable name is a wildcard pattern that matches anything, just as it would be on the left side of an assignment. Edit: It is possible to use constants or variables in a case pattern, but they have to be dotted names to not be treated like a capture pattern. So this would work for your example: class HttpStatus(Enum): NOT_FOUND = 404 match status: case HttpStatus.NOT_FOUND: return "Not found"
- wodenokoto 6y agoDo you know what would happen with: def _id(x): return x not_found = 404 match status: case _id(not_found): return "Not found"
- airstrike 6y agoYes, and this is incredibly disappointing. Couldn't we achieve the same functionality with a little less ambiguity using the following syntax?: not_found = 404 match status: case not_found: return "Not found" case _ as foo: do_something(foo) return "Match anything" it even works for the example in PEP 365 match json_pet: case {"type": "cat", "name": _ as name, "pattern": _ as pattern}: return Cat(name, pattern) case {"type": "dog", "name": _ as name, "breed": _ as breed}: return Dog(name, breed) case _: raise ValueError("Not a suitable pet")
- pfalcon 6y agoI'm with everyone on "incredibly disappointing" valuation. But being pragmatic, I had to accept the idea "it can be addressed later" vs continuing this mess. And there was truly mess, e.g. PEP642, which initially tried to addressed just this issue, turned in a hairy monster trying to random-patch pattern matching considerably in rather weird ways.
- reagle 6y agoI don’t understand this. How are we supposed to read the case word? Is there an online interpreter for this so we can play with it?