input: Write a function to calculate the total price of products in the Products class.
  ```python
  assert calculate_total_price(Products()) == 0
  
  p1 = Product("apple", 1.5)
  p2 = Product("banana", 2.0)
  p3 = Product("orange", 3.0)
  products = Products()
  products.add_product(p1)
  products.add_product(p2)
  products.add_product(p3)
  assert calculate_total_price(products) == 6.5
  
  products = Products()
  products.add_product(Product("book", 10.0))
  products.add_product(Product("pen", 2.5))
  assert calculate_total_price(products) == 12.5
output: class Product:
      def __init__(self, name, price):
          self.name = name
          self.price = price
  
  class Products:
      def __init__(self):
          self.products = []
  
      def add_product(self, product):
          self.products.append(product)
  
  def calculate_total_price(products):
      return sum(product.price for product in products.products)