input: 
  class Rectangle:
      def __init__(self, length, width):
          """ Rectangle class with attributes length and width. """
          self.length = length
          self.width = width
  
      def area(self):
          """ Calculate and return the area of the rectangle.
          >>> rect = Rectangle(5, 10)
          >>> rect.area()
          50
          >>> rect = Rectangle(3, 7)
          >>> rect.area()
          21
          """
          return self.length * self.width
  
output:     
      def perimeter(self):
          """ Calculate and return the perimeter of the rectangle.
          >>> rect = Rectangle(5, 10)
          >>> rect.perimeter()
          30
          >>> rect = Rectangle(3, 7)
          >>> rect.perimeter()
          20
          """
          return 2 * (self.length + self.width)
  