Interesting list Validity (True/False)

[nufuhsus at gmail.com]

On May 11, 5:07 pm, Carsten Haese <cars... at uniqsys.com> wrote:
> On Fri, 2007-05-11 at 12:28 -0700, nufuh... at gmail.com wrote:
> > Hello all,
>
> > First let me appologise if this has been answered but I could not find
> > an acurate answer to this interesting problem.
>
> > If the following is true:
> >     C:\Python25\rg.py>python
> >     Python 2.5.1 (r251:54863, Apr 18 2007, 08:51:08) [MSC v.1310 32
> > bit (Intel)] on
> >     win32
> >     Type "help", "copyright", "credits" or "license" for more
> > information.
> >     >>> [] == []
> >     True
> >     >>> ['-o'] == []
> >     False
> >     >>> ['-o'] == False
> >     False
>
> Your confusion stems from the fact that for a given object, the answer
> to the following three questions can be vastly different:
> a) Is the object identical to True?
> b) Is the object equal to True?
> c) Is the object considered to be True in an "if" statement?
>
> Observe:
>
> >>> def check_trueness(obj):
>
> ...    if obj is True: print repr(obj), "is identical to True."
> ...    else: print repr(obj), "is not identical to True."
> ...    if obj == True: print repr(obj), "is equal to True."
> ...    else: print repr(obj), "is not equal to True."
> ...    if obj: print repr(obj), "is considered to be True by if."
> ...    else: print repr(obj), "is not considered to be True by if."
> ...>>> check_trueness(True)
>
> True is identical to True.
> True is equal to True.
> True is considered to be True by if.>>> check_trueness(1)
>
> 1 is not identical to True.
> 1 is equal to True.
> 1 is considered to be True by if.>>> check_trueness([1])
>
> [1] is not identical to True.
> [1] is not equal to True.
> [1] is considered to be True by if.>>> check_trueness([])
>
> [] is not identical to True.
> [] is not equal to True.
> [] is not considered to be True by if.
>
> Testing whether an object is equal to True is a much stronger test than
> whether it is considered to be True in an 'if' statement, and the test
> for identity is stronger still. Testing whether an object is equal to
> True or identical to True is useless in most Python programs.
>
> So, rather than doing this:
>
> if thing==True:
>    # blah
>
> Just do this:
>
> if thing:
>    # blah
>
> Hope this helps,
>
> --
> Carsten Haesehttp://informixdb.sourceforge.net- Hide quoted text -
>
> - Show quoted text -

Thanks Carsten (& all), I will give the if thing: # blah trick. I
guess I am starting to seem my own confusion. As Grant mentioned, I
was comparing ['-o'] to True which of course is False :o)

However, how would you test for the falsness of the object arg?