[Python-ideas] Please reconsider the Boolean evaluation of midnight

[Amber Yust]

Let's turn this around. Aside from backwards compatibility, what benefit is
there from having midnight evaluate as false?

On Wednesday, March 5, 2014 9:09:50 AM, Skip Montanaro <skip at pobox.com>
wrote:

> On Wed, Mar 5, 2014 at 9:15 AM, Shai Berger <shai at platonix.com> wrote:
> > Also, when opening this thread, I argued that 0 is special,
> > but midnight is not -- which you completely ignore.
>
> Zero is not different, at least when considered as an element of a set
> (of integers, in my example). What's important is that we have a set
> of values (either time objects or integers in these two examples) and
> need some way to specify a sentinel value. That sentinel must not be
> in the set of valid values. In both of these cases, None fills the
> bill. Note that the only reasonable relationship between None and
> either the set of all time objects or the set of all integers is that
> it is not a member of either set. Testing that membership by appealing
> to their value cast to a boolean is simply wrong.
>
> I'll push the argument just a bit further. Suppose you have an
> attribute which corresponds to the setting of a two-valued sensor
> external to your system. You choose to represent those two values in
> your program as True and False. You need a way to tell if any sensor
> inputs have been detected yet, or not, so you initialize the attribute
> with a sentinel value. I don't care what value you choose out of all
> the possible sentinel values available to you (None, [], ["xyz"], {},
> 7, 0.0, etc), treating any of them as a boolean will be wrong. If you
> do, you will erroneously always believe that your sensor has produced
> a value.
>
> I have made this sort of mistake many times over the years, and seen
> other people do it as well. If what you really want to test is
> membership of a value in a set, be explicit about it.
>
> Skip
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