OOP Design

Design a Math Expression Library

import abc
class Expression(abc.ABC):
    @abc.abstractmethod
    def evaluate(self):
        pass
    @abc.abstractmethod
    def simplify(self):
        pass

class Number(Expression):
    def __init__(self, num):
        self.num = num
    def evaluate(self):
        return self.num
    def simplify(self):
        return ascii(self.num)

class Variable(Expression):
    def __init__(self, var, num):
        self.var = var
        self.num = num
    def evaluate(self):
        return self.num
    def simplify(self):
        return self.var

class Parenthersis(Expression):
    def __init__(self, express):
        self.express = express
    def evaluate(self):
        return self.express.evaluate()
    def simplify(self):
        return "(" + self.express.simplify() + ")"

class Operator(Expression):
    pass
class Addition(Operator):
    def __init__(self, right, left):
        self.left, self.right = left, right

    def evaluate(self):
        return self.left.evaluate() + self.right.evaluate()

    def simplify(self):
        if self.left.simplify == "0":
            return self.right.simplify()
        elif self.right.simplify() == "0":
            return self.left.simplify()

        elif self.left.simplify == "0" and self.right.simplify() == "0":
            return "0"

        return self.left.simplify() + "+"  + self.right.simplify()

class Multiplication(Operator):
    def __init__(self, right, left):
        self.left, self.right = left, right
    def evaluate(self):
        return self.left.evaluate() * self.right.evaluate()

    def simplify(self):
        if self.left.simplify == "1":
            return self.right.simplify()
        elif self.right.simplify() == "1":
            return self.left.simplify()
        elif self.left.simplify == "1" and self.right.simplify() == "1":
            return "1"
        return self.left.simplify() + "*" + self.right.simplify()
# Test 
# 5*(a+2)*b+a
a = Variable("a", 1)
b = Variable("b", 2)
num2 = Number(2)
num5 = Number(5)
sub = Multiplication(b, Parenthersis(Addition(num2,a)))
exp  = Addition(a, Multiplication(sub,num5))
print(exp.simplify())
print(exp.evaluate())

# Test
# a*b*(0+a)*1
a = Variable("a", 1)
b = Variable("b", 0)
num1 = Number(1)
num0 = Number(0)
sub = Multiplication(b, Parenthersis(Addition(num0,a)))
exp  = Addition(a, Multiplication(sub,num1))
print(exp.simplify())
print(exp.evaluate())