[Python-Dev] python 3 niggle: None < 1 raises TypeError

[Chris Angelico]

On Fri, Feb 14, 2014 at 7:04 PM, Chris Withers <chris at simplistix.co.uk> wrote:
>
> To implement __lt__ in Python 2, I could do:
>
>     def __lt__(self, other):
>         if not isinstance(other, Range):
>             return True
>         return ((self._lower, self._upper, self._bounds) <
>                 (other._lower, other._upper, other._bounds))
>
> Because None < 1 raises a TypeError, in Python 3 I have to do:
>
>     def __lt__(self, other):
>         if not isinstance(other, Range):
>             return NotImplemented
>         for attr in '_lower', '_upper', '_bounds':
>             self_value = getattr(self, attr)
>             other_value = getattr(other, attr)
>             if self_value == other_value:
>                 pass
>             elif self_value is None:
>                 return True
>             elif other_value is None:
>                 return False
>             else:
>                 return self_value < other_value
>         return False
>
> Am I missing something? How can I get this method down to a sane size?

Can you be certain that all your values are either None or positive
integers? If so, try this:

    def __lt__(self, other):
        if not isinstance(other, Range):
            return True # or NotImplemented, not sure why this change
        return ((self._lower or 0, self._upper or 0, self._bounds or 0) <
                (other._lower or 0, other._upper or 0, other._bounds or 0))

That'll treat all Nones as 0, and compare them accordingly. If you
can't depend on them being positive (eg if you need None to be less
than 0 rather than equal - even more so if you need it to be less than
negative numbers), you'll need to more explicitly check. But this is
nice and tidy, if it works.

ChrisA