[Python-ideas] Fwd: Boolean behavior of None

[Ilkka Pelkonen]

Hi Oleg, others,
It's not that it can't be done, just that it does something you don't
expect. I've been professionally working with C++ for nine years in
large-scale Windows systems, and I do expect a boolean expression return a
boolean value.

Or, can you show me an example how the developer would benefit of the
current behavior? Any operator traditionally considered as boolean will do.

Regards,
Ilkka


On Thu, Jan 17, 2013 at 2:51 PM, Oleg Broytman <phd at phdru.name> wrote:

> On Thu, Jan 17, 2013 at 02:44:03PM +0200, Ilkka Pelkonen <ica at iki.fi>
> wrote:
> > expected_result = (expected_string != 'TRUE') # Boolean
> > element = find_element() # Can return None or an instance of Element
> > flag = (element and element.is_visible())
> > if flag == expected_result:
> > ..# Ok
> > ..return
> > # Otherwise perform some failure related stuff.
> >
> > This code does not work. What happens on the 'flag' assignment row, is
> that
> > if 'element' is None, the expression returns None, not False. This makes
> > the if comparison to fail if expected_result is False, since boolean
> False
> > is not None.
>
>    No need to change the language. Just do
>
> flag = bool(element and element.is_visible())
>
> Oleg.
> --
>      Oleg Broytman            http://phdru.name/            phd at phdru.name
>            Programmers don't die, they just GOSUB without RETURN.
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