input: Write a python function to perform basic arithmetic operations using a Calculator class.
  assert calculator.add(1, 2) == 3
  assert calculator.subtract(5, 2) == 3
  assert calculator.multiply(3, 4) == 12
  assert calculator.divide(10, 2) == 5.0
output: class Calculator:
      def add(self, a, b):
          return a + b
  
      def subtract(self, a, b):
          return a - b
  
      def multiply(self, a, b):
          return a * b
  
      def divide(self, a, b):
          return a / b
  
  calculator = Calculator()