returning True, False or None

[Alex Martelli]

Steven Bethard <steven.bethard at gmail.com> 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?

What about...:

for val in lst:
    if val is not None:
        return val
return None

or the somewhat fancy/clever:

for val in (x for x in lst if x is not None):
    return val
return None


Alex