assign operator to variable in python?

Usual method of applying mathematics to variables is

a * b

Is it able to calculate and manipulate two operands like this?

a = input('enter a value')
b = input('enter a value') 
op = raw_input('enter a operand')

Then how do i connect op and two variables a and b?
I know I can compare op to +, -, %, $ and then assign and compute....

But can i do something like a op b, how to tell compiler that op is an operator?