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Re: Switch statement

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On 3/10/2013 11:18 AM, Steven D'Aprano wrote:
> On Sun, 10 Mar 2013 14:16:27 +0000, Joseph L. Casale wrote:
>
>> I have a switch statement composed using a dict:
>>
>>
>> switch = {
>>      'a': func_a,
>>      'b': func_b,
>>      'c': func_c
>> }
>> switch.get(var, default)()
>>
>>
>> As a result of multiple functions per choice, it migrated to:
>>
>>
>>
>> switch = {
>>      'a': (func_a1, func_a2),
>>      'b': (func_b1, func_b2),
>>      'c': (func_c, )
>> }
>>
>>
>>
>> for f in switch.get(var, (default, )):
>>      f()
>>
>>
>> As a result of only some of the functions now requiring unique
>> arguments, I presume this needs to be migrated to a if/else statement?
>> Is there a way to maintain the switch style with the ability in this
>> scenario to cleanly pass args only to some functions?
>
>
> The dict-as-switch-statement pattern only works when the functions all
> take the same argument(s). Otherwise, you need to check which function
> you are calling, and provide the right arguments.

If, for instance, the functions take either 0 or 1 arg and the 1 arg is 
always the same, an alternative to the other suggestions is to look at 
the signature in an if statement.  In 3.3 this is relatively ease, as 
inspect.signature(func) returns a signature object. There are more 
complicated paths in earlier versions.

-- 
Terry Jan Reedy

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Switch statement "Joseph L. Casale" <jcasale@activenetwerx.com> - 2013-03-10 14:16 +0000
  Re: Switch statement Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-03-10 15:18 +0000
    RE: Switch statement "Joseph L. Casale" <jcasale@activenetwerx.com> - 2013-03-10 17:51 +0000
    Re: Switch statement Terry Reedy <tjreedy@udel.edu> - 2013-03-10 18:02 -0400

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