code: def _FormatExpression(self, frame, expression):
      
      rc, value = _EvaluateExpression(frame, expression)
      if not rc:
        message = _FormatMessage(value['description']['format'],
                                 value['description'].get('parameters'))
        return '<' + message + '>'
  
      return self._FormatValue(value)
docs: Evaluates a single watched expression and formats it into a string form.
  
      If expression evaluation fails, returns error message string.
  
      Args:
        frame: Python stack frame in which the expression is evaluated.
        expression: string expression to evaluate.
  
      Returns:
        Formatted expression value that can be used in the log message.