[Tutor] evaluating AND

[Adam Bark]

On 13/09/2007, Terry Carroll <carroll at tjc.com> wrote:
>
> On Thu, 13 Sep 2007, Orest Kozyar wrote:
>
> > Given a variable x that can either be None or a tuple of two floats [i.e
> .
> > (0.32, 4.2)], which syntax is considered most appropriate under Python
> > coding standards?
> >
> > if x and x[0] > 0:
> >       pass
> >
> > =====OR=====
> >
> > if x:
> >       if x[0] > 0:
> >               pass
>
> I would like either one if instead of "if x" you used "if x is not None";
> that seems a lot easier to me to read.  It's a bit jarring to see the same
> variable used in one expression as both a boolean and a list/tuple.
>
> Besides, suppose somehow x got set to zero.  It would pass without error,
> something you wouldn't want to have happen.  Even if you've set things up
> so that it couldn't happen, it's not obvious from looking at this code
> that it couldn't happen.
>
> If you really want to test for x being non-None, test for x being
> non-None.


The problem is what if it's an empty list or tuple? It would pass but have
not value
whereas if x would work fine.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.python.org/pipermail/tutor/attachments/20070913/2cffd709/attachment.htm