OT: Re: Just took a look in the perl newsgroup....

[Bengt Richter]

On Wed, 28 May 2003 14:17:37 -0600, Steven Taschuk <staschuk at telusplanet.net> wrote:

>Quoth Bengt Richter:
>  [...]
>> IMO that's still a workaround for the case (;-) where you want to rebind
>> in the same scope. But I just thought of an alternative, which see below
>> in stripped-down version of previous example:
>  [...]
>>         ## a local case structure with rebinding in local scope
>>         try: raise `x`
>>         except '1':
>>             # case code in same scope as case
>>             inner_var = '<<value bound in scope of "case" 1)>>'
>>         except '2':
>>             inner_var = '<<value bound in scope of "case" 2>>'
>>         except:
>>             inner_var = '<<value bound in scope of "case" default>>'
>
>Yikes.
>
>Inherently fragile due to reliance on interning of repr(x).  Won't
>work at all if/when string exceptions go away.
Which version requires interning of repr(x)? It looks like the code is less
efficient than the corresponding if/elif/else code, however.

>
>A strong candidate for a Most Outlandish Proposal award.  (In
>fact, I think you're a strong candidate for a Lifetime Achievement
>Award in this area.  <0.25 wink>)
>
LOL ;-)
I figure the best QA for toys is playing with them ;-)

Responding to the objections above <~ ^ @>

====< ycase.py >=====================================
class Switch(object):
    def __init__(self, *caseNames):
        for name in caseNames:
            if not isinstance(name,str): name = `name`
            exec ('class _%s(Exception):pass'%name) in self.__dict__
            del self.__dict__['__builtins__']
    def __call__(self, name):
        raise getattr(self, '_%s'%name, ValueError)

case = switch = Switch(1,2,'foo')

def f(x):
    def g(x):
        inner_var = 5      
        ## a local case structure with rebinding in local scope
        try: switch(x)
        except case._1:
            # case code in same scope as case
            inner_var = '<<value bound in scope of "case" 1)>>'
        except case._2:
            inner_var = '<<value bound in scope of "case" 2>>'
        except case._foo:
            inner_var = '<<value bound in scope of "case" foo>>'
        except:
            inner_var = '<<value bound in scope of "case" default>>'
        print 'inner_var as seen at end of "case":', inner_var
    g(x)

for i in (0,1,2,'foo'): print '---- f(%r) -----'%i; f(i)
=====================================================
[19:59] C:\pywk\clp>ycase.py
---- f(0) -----
inner_var as seen at end of "case": <<value bound in scope of "case" default>>
---- f(1) -----
inner_var as seen at end of "case": <<value bound in scope of "case" 1)>>
---- f(2) -----
inner_var as seen at end of "case": <<value bound in scope of "case" 2>>
---- f('foo') -----
inner_var as seen at end of "case": <<value bound in scope of "case" foo>>

;-)

Regards,
Bengt Richter