Interesting list Validity (True/False)

[nufuhsus at gmail.com]

On May 11, 5:12 pm, nufuh... at gmail.com wrote:
> 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?- Hide quoted text -
>
> - Show quoted text -

Would that be arg is not True: # blah.?