[Python-Dev] Switch statement

[Delaney, Timothy (Tim)]

Guido van Rossum wrote:

> I wonder if there should be two default clauses, or some other
> syntactic way to indicate whether we expect all x to be hashable?

    switch expr:
        case 1:
            statements
        case 2:
            statements
        else:
            statements
        except KeyError:
            statements
        finally:
            statements

    switch expr:
        case 1:
            statements
        case 2:
            statements
        else:
            statements
    except KeyError:
        statements
    finally:
        statements

:)

Seriously, I think I'd rather be explicit and just have KeyError
propagate. If someone is expecting occasional unhashable values, they
can just wrap it in try/except.

    try:
        switch expr:
            case 1:
                statements
            case 2:
                statements
            else:
                statements
    except KeyError:
        statements
    finally:
        statements

The first syntax though does have the advantage that it could catch only
KeyErrors raised from the switch statement. That could be easily handled
by a separate SwitchKeyError exception (inheriting from KeyError).

Tim Delaney