Sum with __repr__

Define a class Sum with a constructor that takes two arguments, left, and right. The constructor should set corresponding fields on the object, i.e., the field left should get the value from left and the field right should get the value from right. You should set a third field, sum, that is equal to the sum of the two fields.

Define a __repr__ method that reproduces the constructor, i.e.,

>>> Sum(1, 2)
Sum(1, 2)

and a __str__ method that shows the sum, i.e.,

>>> print(Sum(1, 2))
1 + 2 = 3