input: Write a function to implement a Python class called Rectangle 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.
  assert Rectangle(5, 10).area()==50
  assert Rectangle(3, 4).area()==12
  assert Rectangle(7, 2).area()==14
  assert Rectangle(10, 5).area()==50
output: class Rectangle:
      def __init__(self, length, width):
          self.length = length
          self.width = width
      
      def area(self):
          return self.length * self.width