[Python-Dev] Switch statement (original) (raw)

Fredrik Lundh fredrik at pythonware.com
Thu Jun 22 18:22:17 CEST 2006

Guido van Rossum wrote:

which simply means that expr will be evaluated at function definition time, rather than at runtime. example usage:

var = expression if var == constant sre.FOO: ... elif var == constant sre.BAR: ... elif var in constant (sre.FIE, sre.FUM): ... This gets pretty repetitive. One might suggest that 'case' could imply 'constant'...?

possibly, but I find that a tad too magic for my taste.

a "constant" (or perhaps better, "const") primary would also be useful in several other cases, including:

an alternative would be to add a const declaration that can only be used in local scopes; i.e.

 def foo(value):
    const bar = fie.fum
    if value == bar:
       ...

which would behave like

 def foo(value, bar=fie.fum):
    if value == bar:
        ...

but without the "what if we pass in more than one argument?" issue.

yet another alternative would be a const declaration that you could use on a global level, but I fail to see how you could propagate the "const- ness" property to whoever wants to use a const object -- unless, of course, you implement

 const bar = fie.fum

 def foo(value):
    if value == bar:
       ...

as

 class constant_wrapper(object):
     def __init__(self, value):
         self.value = value

 bar = constant_wrapper(fie.fum)

 def foo(value, bar=bar.value):
     if value == bar:
         ...

(except for the default argument thing; see above). the result is a kind of semi-constant objects that would be useful, but perhaps not constant enough...)

it might be too much C# exposure, but I think I prefer the "explicit when using" approach...

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