[Python-Dev] Re: PEP 622: Structural Pattern Matching

2020年6月23日 12:33:31 -0700

On 23/06/2020 17:01, Guido van Rossum wrote:
You can combine several literals in a single pattern using `|` ("or"):
```py
    case 401|403|404:
      return "Not allowed"
The PEP is great, but this strikes me as horribly confusing, given that 401|403|404 is already legal syntax. IIUC any legal expression can come between `case` and `:`, but expressions that contain `|` at their outermost level are *interpreted differently* than from in other contexts.
Presumably adding parentheses:
  case (401|403|404):
would make it equivalent to
  case 407:
Is a separator (other than whitespace) actually needed? Can the parser cope with
  case 401 403 404:
Failing that IMO preferable, albeit not ideal, possibilities would be
 1) Use colon as the separator.
2) Use comma as the separator - this is already legal syntax too, but IMO it reads more naturally. (And IIRC there are already contexts where brackets are necessary to indicate a tuple.)
Perhaps someone can think of something better.
I also (with others) prefer `else:` or perhaps `case else:` to using the`_` variable. The latter is obscure, and woudn't sit well with code that already uses that variable for its own purposes.
Rob Cliffe
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