code: def markInputline( self, markerString = ">!<" ):
          
          line_str = self.line
          line_column = self.column - 1
          if markerString:
              line_str = "".join((line_str[:line_column],
                                  markerString, line_str[line_column:]))
          return line_str.strip()
docs: Extracts the exception line from the input string, and marks
             the location of the exception with a special symbol.