input: Write a python function to demonstrate the difference between a function and a method in Python by creating a simple class with a method and a standalone function.
  assert standalone_function(5) == 10
  assert my_class_instance.method() == 20
output: class MyClass:
      def method(self):
          return 20
  
  def standalone_function(x):
      return x * 2
  
  my_class_instance = MyClass()