old_contents: import abc
  
  # For 2 and 3 compatibility
  # https://stackoverflow.com/questions/35673474/
  ABC = abc.ABCMeta('ABC', (object,), {'__slots__': ()})
  
  
  class BaseOfficeFile(ABC):
      def __init__(self):
          pass
  
      @abc.abstractmethod
      def load_key(self):
          pass
  
      @abc.abstractmethod
      def decrypt(self):
          pass
  
new_contents: import abc
  
  # For 2 and 3 compatibility
  # https://stackoverflow.com/questions/35673474/
  ABC = abc.ABCMeta('ABC', (object,), {'__slots__': ()})
  
  
  class BaseOfficeFile(ABC):
      def __init__(self):
          pass
  
      @abc.abstractmethod
      def load_key(self):
          pass
  
      @abc.abstractmethod
      def decrypt(self):
          pass
  
      @abc.abstractmethod
      def is_encrypted(self):
          pass
  
subject: Add is_encrypted() to abstract methods