Python Basic Doubt

Sat Aug 10 12:40:40 EDT 2013

On 2013年08月10日 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