[Tutor] "x and y" means "if x is false, then x, else y"??
Adam Bark
adam.jtm30 at gmail.com
Mon Jul 5 14:21:21 CEST 2010
On 5 July 2010 12:53, Richard D. Moores <rdmoores at gmail.com> wrote:
> On Mon, Jul 5, 2010 at 04:09, Stefan Behnel <stefan_ml at behnel.de> wrote:
> > Richard D. Moores, 05.07.2010 11:37:
> >>
> >> I keep getting hung up over the meaning of "the return
> >> value" of an expression. I am of course familiar with values returned
> >> by a function, but don't quite grasp what the return value of, say,
> >> the y of "x and y" might mean.
> >
> > Think of a different expression, like "1+1". Here, the return value (or
> > maybe a better wording would be the result value) is 2.
> >
> >
> >> Also, you distinguish between a return value of True and and the value
> >> of y being such (say 5, and not 0) that it makes y true (but not
> >> True). So another thing I need to know is the difference between True
> >> and true. Also between False and false. And why the difference is
> >> important.
> >
> > "True" is the value "True" in Python, which is a singleton. You can test
> for
> > it by using
> >
> > x is True
>
> Ah. But could you give me an x that would satisfy that? I can think of
>
> >>> (5 > 4) is True
> True
>
> But how can (5 > 4) be an x? Could you show me some code where it could be?
>
> >>> x = (5 > 4)
> >>> x
> True
> >>> x is True
> True
>
> So it can! That surprised me. I was expecting "x = (5 > 4)" to be
> absurd -- raise an exception? Still seems pretty weird.
>
Greater than (>) works like the mathematical operators in returning a value,
it just happens that for comparison operators (>, <, ==, !=) the values can
only be True or False.
HTH,
Adam.
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