input: Write a python function to create a factory that returns objects of Triangle and Rectangle classes and then call their type methods.
  assert f.get_obj("triangle").sides == 3
  assert f.get_obj("rectangle").sides == 4
output: class Triangle:
      def __init__(self):
          self.sides = 3
  
  class Rectangle:
      def __init__(self):
          self.sides = 4
  
  class Factory:
      def get_obj(self, shape_type):
          if shape_type.lower() == "triangle":
              return Triangle()
          elif shape_type.lower() == "rectangle":
              return Rectangle()
          else:
              raise ValueError("Unknown shape type")
  
  f = Factory()