True of False - Python

On Sep 27, 11:33 am, kou...@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?
> Thanks.
>
> Kou

,
You may want to include paren around ("c" in a) and a lower case p for
Print, i.e. print, and it should work

so eg:
a = ["a", "b", "c", "d", "e", "f"]

if ("c" in a) == True:
print "Yes"

On Thu, 27 Sep 2007 09:33:34 -0700, koutoo 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?

Wow that's odd:

In [265]: a = list('abcdef')

In [266]: a
Out[266]: ['a', 'b', 'c', 'd', 'e', 'f']

In [267]: 'c' in a
Out[267]: True

In [268]: 'c' in a == True
Out[268]: False

In [269]: ('c' in a) == True
Out[269]: True

In [270]: 'c' in (a == True)
---------------------------------------------------------------------------
<type 'exceptions.TypeError'> Traceback (most recent call last)

/home/bj/<ipython console> in <module>()

<type 'exceptions.TypeError'>: argument of type 'bool' is not iterable


What's going on there?

Ciao,
Marc 'BlackJack' Rintsch

On 9/27/07, koutoo@hotmail.com <koutoo@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>.

--
Cheers,
Simon B.
simon@brunningonline.net

kou...@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?
> Thanks.
>
> Kou

Hello,
Just try :

a = ["a","b","c","d","e","f"]
if "c" in a:
print "yes"

That is going to work as the statement '"c" in a' itself is true. You
could try that by typing "c" in a at the interpreter.

regards,
Shriphani Palakodety

On Sep 27, 12:48 pm, "Simon Brunning" <si...@brunningonline.net>
wrote:
> On 9/27/07, kou...@hotmail.com <kou...@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

Marc 'BlackJack' Rintsch <bj_666@gmx.net> wrote:

> In [268]: 'c' in a == True
> Out[268]: False
>
> In [269]: ('c' in a) == True
> Out[269]: True
>
> In [270]: 'c' in (a == True)
> -----------------------------------------------------------------------
> ----
><type 'exceptions.TypeError'> Traceback (most recent call
>last)
>
> /home/bj/<ipython console> in <module>()
>
><type 'exceptions.TypeError'>: argument of type 'bool' is not iterable
>
>
> What's going on there?

See http://docs.python.org/ref/comparisons.html

> Comparisons can be chained arbitrarily, e.g., x < y <= z is equivalent
> to x < y and y <= z, except that y is evaluated only once (but in both
> cases z is not evaluated at all when x < y is found to be false).

In exactly the same way:

'c' in a == True

is equivalent to:

'c' in a and a == True

which is False.

koutoo@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?
> Thanks.

You are unnecessarily adding a comparison with True. The correct way to
write that is

if "c" in a:
print "yes"

Bu of course you haven't actually told us what you really did, because
the code you represent has syntax errors.

>>> a = ["a", "b", "c", "d", "e", "f"]
>>> "c" in a
True
>>> if "c" in a == True:
.... print "found it"
....
>>> if ("c" in a) == True:
.... print "At last!"
....
At last!
>>>
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden

Sorry, the dog ate my .sigline

On 27/09/2007, Casey <Caseyweb@gmail.com> wrote:
> On Sep 27, 12:48 pm, "Simon Brunning" <si...@brunningonline.net>
> wrote:
> > On 9/27/07, kou...@hotmail.com <kou...@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
>

On Thu, 2007-09-27 at 16:47 +0000, Marc 'BlackJack' Rintsch wrote:
> On Thu, 27 Sep 2007 09:33:34 -0700, koutoo 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?
>
> Wow that's odd:
>
> In [265]: a = list('abcdef')
>
> In [266]: a
> Out[266]: ['a', 'b', 'c', 'd', 'e', 'f']
>
> In [267]: 'c' in a
> Out[267]: True
>
> In [268]: 'c' in a == True
> Out[268]: False
>
> In [269]: ('c' in a) == True
> Out[269]: True
>
> In [270]: 'c' in (a == True)
> ---------------------------------------------------------------------------
> <type 'exceptions.TypeError'> Traceback (most recent call last)
>
> /home/bj/<ipython console> in <module>()
>
> <type 'exceptions.TypeError'>: argument of type 'bool' is not iterable
>
>
> What's going on there?

What's going on here is that both 'in' and '==' are comparison
operations, and Python allows you to chain comparisons. Just like "a < x
< b" is evaluated as "a < x and x < b", "'c' in a == True" is evaluated
as "'c' in a and a == True". Obviously, since a==True is false, the
chained comparison is False.

--
Carsten Haese
http://informixdb.sourceforge.net