input: Write a python function to implement a basic calculator class with methods for addition, subtraction, multiplication, and division.
  assert calc.add(10, 2) == 12
  assert calc.subtract(10, 2) == 8
  assert calc.multiply(10, 2) == 20
  assert calc.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):
          if b == 0:
              raise ValueError("Cannot divide by zero")
          return a / b
  
  calc = Calculator()