input: Write a function to create a Python class called Rectangle that represents a two-dimensional rectangle with a length and width. The class should have an `__init__` method to initialize the length and width, and an `area` method to calculate and return the area of the rectangle.
  assert Rectangle(4, 5).area() == 20
  assert Rectangle(7, 3).area() == 21
  assert Rectangle(2, 2).area() == 4
  assert Rectangle(0, 5).area() == 0
  assert Rectangle(1, 1).area() == 1
output: class Rectangle:
      def __init__(self, length, width):
          self.length = length
          self.width = width
      
      def area(self):
          return self.length * self.width