[PyQt] QPyNullVariant and bool()

[Deniz Turgut]

On Wed, Apr 25, 2012 at 3:26 AM, Phil Thompson
<phil at riverbankcomputing.com> wrote:
> On Tue, 24 Apr 2012 14:28:02 -0400, Deniz Turgut <dturgut at gmail.com>
> wrote:
>> Would it be logical to add a __nonzero__ method to QPyNullVariant
>> which always returns False?
>>
>> I was going through a code of mine which broke with a new version of
>> PyQt. I realized that it was because there is no __nonzero__ method in
>> QPyNullVariant so bool(QPyNullVariant) is always True.
>>
>> Right now, if you use QVariant api 2, you can't check nicely (without
>> typechecking) whether you get a nonzero value or Null/Falsy value.
>
> From a purist point of view I don't associate Null with False (or with
> True either but the current behaviour reflects the Python default).
>
> From a portability point of view it's a change in the API.
>
> From a pragmatic point of view I need to be persuaded - I've not been
> affected by the issue myself.

Actually, pragmatic part is not much of a big deal. Although it looks
a bit ugly to me, I can live with code like:

if value and not isinstance(value, QtCore.QPyNullVariant):
   do_something_with(value)

Or I could deal with it much before, and eliminate a Null possibility.

I guess my issue is closer to the purist view. I do agree that Null is
neither True, nor False, but I'd expect it to behave like None. It is
not False but rather Falsy. That's why, I spent some time figuring out
why a test like 'if value:' was passing when a Null was returned.

 --
 Deniz