input: Write a function to create a Rectangle class that represents a two-dimensional rectangle with a length and width. The class should have an initialization method to set the length and width, and a method to calculate 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(7, 9).area()==63
  assert Rectangle(1, 1).area()==1
  assert Rectangle(0, 10).area()==0
  assert Rectangle(3, 3).area()==9
output: class Rectangle:
      def __init__(self, length, width):
          self.length = length
          self.width = width
  
      def area(self):
          return self.length * self.width