old_contents: from person import Person
  
  __all__ = ['AddressBook']
  
  
  class AddressBook(object):
  
      def __init__(self):
          self.persons = []
  
      def add_person(self, person):
          self.persons.append(person)
  
      def __contains__(self, item):
          if isinstance(item, Person):
              return item in self.persons
          return False
  
new_contents: from person import Person
  
  __all__ = ['AddressBook']
  
  
  class AddressBook(object):
  
      def __init__(self):
          self.persons = []
          self.groups = []
  
      def add_person(self, person):
          self.persons.append(person)
  
      def add_group(self, group):
          self.groups.append(group)
  
      def __contains__(self, item):
          if isinstance(item, Person):
              return item in self.persons
          return False
  
subject: Add `add_group` method to `AddressBook` class - to make it possible to add groups to the address book