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Re: Python Basic Doubt

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  Re: Python Basic Doubt Krishnan Shankar <i.am.songoku@gmail.com> - 2013-08-11 08:39 +0530

#52348 — Re: Python Basic Doubt

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Thanks Tim,

This takes me to one more question.

'is' operator is used to compare objects and it should not be used to
compare data.

So can it be compared with 'False'.

i.e. Is this code possible

if a is False:
    print 'Yes'
if b is False:
    print 'No'

Because i recommended this should not be done. But my colleagues say it is
correct.

Regards,
Krishnan


On Sat, Aug 10, 2013 at 10:10 PM, Tim Chase
<python.list@tim.thechases.com>wrote:

> On 2013-08-10 21:03, Krishnan Shankar wrote:
> > >>> a=10
> > >>> id(a)
> > 21665504
> > >>> b=a
> > >>> id(b)
> > 21665504
> > >>> c=10
> > >>> id(c)
> > 21665504
> >
> > I am actually assigning new value to c. But from the value of id()
> > all three variables take same location. With variables a and b it
> > is ok. But why c taking the same location?
>
> As an internal optimization, CPython caches small integer values
>
>   >>> a = 256
>   >>> b = 256
>   >>> a is b
>   True
>   >>> a = 257
>   >>> b = 257
>   >>> a is b
>   False
>
> Because it's an internal implementation detail, you shouldn't count
> on this behavior (Jython or Cython or IronPython may differ; or
> future versions of Python may cache a different range of numbers).
>
> Generally, if you are using the "is" operator to compare against
> anything other than None, you're doing it wrong. There are exceptions
> to this, but it takes knowing the particulars.
>
> -tkc
>
>
>
>

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