old_contents: """
  Error heirarchy for stratis cli.
  """
  
  class StratisCliError(Exception):
      """
      Top-level stratis cli error.
      """
      pass
  
  
  class StratisCliValueError(StratisCliError):
      """ Raised when a parameter has an unacceptable value.
  
          May also be raised when the parameter has an unacceptable type.
      """
      _FMT_STR = "value '%s' for parameter %s is unacceptable"
  
      def __init__(self, value, param, msg=None):
          """ Initializer.
  
              :param object value: the value
              :param str param: the parameter
              :param str msg: an explanatory message
          """
          # pylint: disable=super-init-not-called
          self._value = value
          self._param = param
          self._msg = msg
  
      def __str__(self): # pragma: no cover
          if self._msg:
              fmt_str = self._FMT_STR + ": %s"
              return fmt_str % (self._value, self._param, self._msg)
          else:
              return self._FMT_STR % (self._value, self._param)
  
  
  class StratisCliValueUnimplementedError(StratisCliValueError):
      """
      Raised if a parameter is not intrinsically bad but functionality
      is unimplemented for this value.
      """
      pass
  
  class StratisCliUnimplementedError(StratisCliError):
      """
      Raised if a method is temporarily unimplemented.
      """
      pass
  
new_contents: """
  Error heirarchy for stratis cli.
  """
  
  class StratisCliError(Exception):
      """
      Top-level stratis cli error.
      """
      pass
  
  
  class StratisCliValueError(StratisCliError):
      """ Raised when a parameter has an unacceptable value.
  
          May also be raised when the parameter has an unacceptable type.
      """
      _FMT_STR = "value '%s' for parameter %s is unacceptable"
  
      def __init__(self, value, param, msg=None):
          """ Initializer.
  
              :param object value: the value
              :param str param: the parameter
              :param str msg: an explanatory message
          """
          # pylint: disable=super-init-not-called
          self._value = value
          self._param = param
          self._msg = msg
  
      def __str__(self): # pragma: no cover
          if self._msg:
              fmt_str = self._FMT_STR + ": %s"
              return fmt_str % (self._value, self._param, self._msg)
          else:
              return self._FMT_STR % (self._value, self._param)
  
  
  class StratisCliValueUnimplementedError(StratisCliValueError):
      """
      Raised if a parameter is not intrinsically bad but functionality
      is unimplemented for this value.
      """
      pass
  
  class StratisCliUnimplementedError(StratisCliError):
      """
      Raised if a method is temporarily unimplemented.
      """
      pass
  
  class StratisCliKnownBugError(StratisCliError):
      """
      Raised if a method is unimplemented due to a bug.
      """
      pass
  
subject: Add a class for a known error that prevents implementation.