old_contents: #!/usr/bin/env python3
  """Classes and methods for working with PDA configurations."""
  
  import collections
  
  
  class PDAConfiguration(collections.namedtuple(
      'PDAConfiguration',
      ['state', 'remaining_input', 'stack']
  )):
      """
      A configuration is a triple of current state, remaining input and stack.
  
      It represents the complete runtime state of a PDA.
      It is hashable and immutable.
      """
  
      def copy(self):
          """
          Return a deep copy of the PDA configuration.
  
          As this class is immutable, this has no effect.
          """
          return self
  
      def __repr__(self):
          """Return a string representation of the configuration."""
          return '{}({})'.format(self.__class__.__name__, self.__dict__)
  
new_contents: #!/usr/bin/env python3
  """Classes and methods for working with PDA configurations."""
  
  import collections
  
  
  class PDAConfiguration(collections.namedtuple(
      'PDAConfiguration',
      ['state', 'remaining_input', 'stack']
  )):
      """
      A configuration is a triple of current state, remaining input and stack.
  
      It represents the complete runtime state of a PDA.
      It is hashable and immutable.
      """
  
      def copy(self):
          """
          Return a deep copy of the PDA configuration.
  
          As this class is immutable, this has no effect.
          """
          return self
  
      def __repr__(self):
          """Return a string representation of the configuration."""
          return '{}({}, {}, {})'.format(
              self.__class__.__name__,
              self.state,
              self.remaining_input,
              self.stack
          )
  
subject: Fix PDAConfiguration.__repr__