Regarding the magical "or" operator

[David Ascher]

Hi Tom!

On 14 Aug 1999, Tom Christiansen wrote:

> I was wondering how often most python programmers make use of that
> remarkably nifty property of the logical operators, in which they
> produce not merely 0 or 1, but the value is last looked at when it
> decided whether the expression was true or false.

I'm not sure about most python programmers.  It's a feature of the
language that I always teach in my courses, and I tend to get blank looks
at first.  I find that once I motivate the or behavior with an example
like:

    title = windowname or 'Untitled'

a few folks think it's neat (and I guess from that that they plan on using
it, or at least trying it).  I use it periodically, although not very
often.

Not that you asked, but I find the 'and' behavior much harder to motivate
and grok, and I avoid it personally.

> My question is this: have you ever had an urge for it (or a variant)
> to care about the difference between None and any other false value?
[...]
> The idea would be a version of "or" that would return the first non-None
> value.  For example, supposing this were called "nor" (silly name,
> but this is *not* a proposal):
> 
> 	print f() nor h()
>     []
> 
> 	print g() nor h()
>     ['Some']
> 
> The argument is that this would be used not with prints, but with
> assignments, as in
> 
>     a = f() nor g()
> 
> The reason I ask is not because I actually want such a thing.  Gosh, no.
> I'm rather uncomfortable with the idea.  I'm just trying to gather some
> understanding and perspective for use with the folks who *would* like
> such an oddity. :-)

FWIW, it doesn't grab me.  I'd read 'a nor b' as 'not (a or b)', and I
know too much about truth and falsehood in Python to expect None to be
treated differently.

(It's a nice word, though.  One that, alas, Dr. Seuss didn't use when he
should have in One Fish, Two Fish, Red Fish, Blue Fish.)

--david ascher