'11' + '1' is '111'?

[MRAB]

Benjamin Peterson wrote:
> metal <metal29a <at> gmail.com> writes:
> 
>> '11' + '1' == '111' is well known.
>>
>> but it suprises me '11'+'1' IS '111'.
>>
>> Why? Obviously they are two differnt object.
>>
>> Is this special feature of imutable object?
> 
> As other posters have pointed out, CPython does cache some small strings. In
> this case, however, it's because '1' + '11' is constant folded.
> 
It's also easy to fool the constant folding:

 >>> '11' + '1' is '111'
True
 >>> '11' * 1 + '1' is '111'
True
 >>> '11' + '1' * 1 is '111'
False