new_contents: class PhoneBook:
      def __init__(self):
          self.numbers = dict()
  
      def insert(self, name, number):
          self.numbers[name] = number
  
      def remove(self, name):
          del self.numbers[name]
  
      def lookup(self, name):
          if name in self.numbers:
              return self.numbers[name]
          else:
              return 'NOT FOUND'
  
      def list(self):
          names = list(self.numbers.keys())
          names.sort()
          for name in names:
              print("{} {}".format(name, self.numbers[name]))
  
  
  def main():
      pass
  
  
  if __name__ == '__main__':
      main()
  
subject: add phone_book_2.py, dict realization