True of False

[Richard Thomas]

On 27/09/2007, Casey <Caseyweb at gmail.com> wrote:
> On Sep 27, 12:48 pm, "Simon Brunning" <si... at brunningonline.net>
> wrote:
> > On 9/27/07, kou... at hotmail.com <kou... at hotmail.com> wrote:
> >
> > > I tried writing a true and false If statement and didn't get
> > > anything?  I read some previous posts, but I must be missing
> > > something.  I just tried something easy:
> >
> > > a = ["a", "b", "c", "d", "e", "f"]
> >
> > > if "c" in a == True:
> > >      Print "Yes"
> >
> > > When I run this, it runs, but nothing prints.  What am I doing wrong?
> >
> > Just use
> >
> > if "c" in a:
> >
> > and all will be well. The True object isn't the only truthy value in
> > Python - see <http://docs.python.org/lib/truth.html>.
>
> I would recommend the OP try this:
>
> run the (I)python shell and try the following:
>
> >>> a = [x for x in "abcdefg"]
> >>> a
> ['a','b','c','d','e','f','g']
> >>> "c" in a
> True
> >>> "c" in a == True
> False
> >>> ("c" in a) == True
> True
>
> The reason your conditional failed is that it was interpreted as "c"
> in (a == True) which is False.
> the "==" operator binds at a higher precedence level than the "in"
> operator, just as multiplication
> binds higher than addition
>

Actually it evaluates '("c" in a) and (a == True)'. You can check like so:

import dis
a = list("abcdef")
dis.dis(lambda: "c" in a == True)

And just follow the bytecode operations.

-- Richard.

> --
> http://mail.python.org/mailman/listinfo/python-list
>