returning True, False or None

[Steve Holden]

Steven Bethard wrote:

> I have lists containing values that are all either True, False or None, 
> e.g.:
> 
>     [True,  None,  None,  False]
>     [None,  False, False, None ]
>     [False, True,  True,  True ]
>     etc.
> 
> For a given list:
> * If all values are None, the function should return None.
> * If at least one value is True, the function should return True.
> * Otherwise, the function should return False.
> 
> Right now, my code looks like:
> 
>     if True in lst:
>         return True
>     elif False in lst:
>         return False
>     else:
>         return None
> 
> This has a light code smell for me though -- can anyone see a simpler 
> way of writing this?
> 
> STeVe

That code looks like a pretty solid implementation of the spec to me. 
There isn't a strict need for the last else, of course, which may be the 
smell you detect.

If you wanted to get clever you could write something like

for i in True, False:
   if i in lst:
     return i
return False

but frankly I think that's more obscure, and saves you pretty much nothing.

regards
  Steve
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