input: Write a function to create a Python class called Rectangle with a constructor that initializes the length and width of the rectangle. The class should have a method called area that returns the area of the rectangle.
  
  class Rectangle:
      def __init__(self, length, width):
          self.length = length
          self.width = width
  
      def area(self):
          return self.length * self.width
  
  assert Rectangle(4, 5).area()==20
  assert Rectangle(3, 7).area()==21
  assert Rectangle(0, 5).area()==0
  assert Rectangle(10, 10).area()==100
output: class Rectangle:
      def __init__(self, length, width):
          self.length = length
          self.width = width
  
      def area(self):
          return self.length * self.width