[Tutor] Where to put small auxiliary function

[Mark Lawrence]

On 20/07/2012 11:07, Jose Amoreira wrote:
> Hi.
> This is a question about style. I have a class definition that calls a
> small auxiliary function. Because this function isn't used anywhere
> else, I'd like to include it inside the class definition. However, if
> I do that, I'll have to use "self" in the call argument, which is (I
> think) rather awkward.
> Let me give an example:
>
> def is_odd(k):
>      if k % 2 == 0:
>          return False
>      else:
>          return True

I'll point out before anyone else does that you can write this function 
as a one line return.  I'll leave you to work out how.  Personally I 
prefer the longer version but each to their own.

>
> class MyOddNbr(object):
>      def __init__(self, k):
>          if is_odd(k):
>              self.k = k
>          else:
>              self.k = k + 1
>
> This works fine, but I'd like to have is_odd defined inside the class
> definition, because that's the only context where that function is
> used. That would be something like
>
> class MyOddNbr(object):
>      def is_odd(self,k):
>          if k % 2 == 0:
>              return False
>          else:
>              return True
>      def __init__(self,k):
>          if self.is_odd(k):
>              self.k = k
>          else:
>              self.k = k + 1
>
> This also works fine, but the function is_odd() is so simple and
> generic that I find it strange to define it with is_odd(self,k) or to
> call it with is_odd(self,k).
> What is the pythonic way of doing this kind of stuff?

Don't put it in the class.  It's a general purpose function that can be 
used anywhere so keep it at the module level.

> Thanks.
> Ze
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-- 
Cheers.

Mark Lawrence.