On 2020年06月23日 20:27, Rob Cliffe via Python-Dev wrote:
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.
The grammar shows that 'case' is followed by a series of alternatives,
separated by '|', but the alternatives aren't expressions, basically
only literals and instances of a given class. You can't say "case 1 +
2:", for example.
Presumably adding parentheses:
case (401|403|404):
would make it equivalent to
case 407:
I'm not sure whether that's legal, but it's not equivalent.
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.
I think that's done for consistency. '_' is a wildcard and you can have:
case (_, _):
to match any 2-tuple, so:
case _:
would match any value, and can thus already serve as the default.
I wouldn't object to 'else', though.
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