On 08/10/2013 08:09 PM, Krishnan Shankar wrote:
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'
Depends on what you want. If you want to differentiate between a value
of False, and other false-like values 0, (), [], {} and so on, then you
need to be explicit with
if a is False:
Normally, that's not what you want, so you use
if not a:
to catch any of those false-like values.
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.l...@tim.thechases.com <mailto:python.l...@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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