Is behavior of += intentional for int?

[zaur]

On 29 авг, 16:45, zaur <szp... at gmail.com> wrote:
> Python 2.6.2 (r262:71600, Apr 16 2009, 09:17:39)
> [GCC 4.0.1 (Apple Computer, Inc. build 5250)] on darwin
> Type "copyright", "credits" or "license()" for more information.>>> a=1
> >>> x=[a]
> >>> id(a)==id(x[0])
> True
> >>> a+=1
> >>> a
> 2
> >>> x[0]
>
> 1
>
> I thought that += should only change the value of the int object. But
> += create new.
> Is this intentional?

As a result of this debate is not whether we should conclude that
there should be two types of integers in python: 1) immutable numbers,
which behave as constant value; 2) mutable numbers, which behave as
variable value?