What is if(e & 1) means in python?

Question

So I was reading a question on SO and I don't understand the code of the answer it has. It is doing some bit wise operation but i don't know how that works and what is actually going on within the while loop and the need of mod at b2 = (b2*b2) % m

        b2 = b                         
        res = 1                        
         while e:                       
            if e & 1:                  
                res = (res * b2) % m   
            b2 = (b2*b2) % m        
            e >>= 1

Can anyone help me to understand it ?

This is the question

Answer 1

It is a bitwise AND operation. In bitwise binary operations, the two numbers in their binary form are processed by their corresponding bits. So 1 is only one bit. It will be compared to last bit of a number. So a&1 will return 1 if last bit of 1 is 1 and zero otherwise. So the if block will be executed accordingly eg 12 AND 1
1 1 0 0
0 0 0 1
_________
0 0 0 0