why string multiplied by and integer and variable multiplied by integer is not same?

Question

Suppose on the following example:

a='a'

while multiplying by an integer both a*2 and 'a' *2 yields same result

>>a*2
'aa'
>>'a' *2 
'aa'

however this does not hold same for comparing:

>>a*2 is 'aa'
False
>>'a' * 2 is 'aa'
True
>> a*2 is 'a' *2
False