code: def __convert_string_type(self, p_c_tuple):
          # type: (Tuple[text_type,...])->Tuple[text_type]
          
          if not isinstance(p_c_tuple, tuple):
              raise Exception('Pos condition expects tuple of string. However = {}'.format(p_c_tuple))
  
          converted = [text_type] * len(p_c_tuple)
          for i, pos_element in enumerate(p_c_tuple):
              if six.PY2 and isinstance(pos_element, str):
                  """str into unicode if python2.x"""
                  converted[i] = pos_element.decode(self.string_encoding)
              elif six.PY2 and isinstance(pos_element, text_type):
                  converted[i] = pos_element
              elif six.PY3:
                  converted[i] = pos_element
              else:
                  raise Exception()
  
          return tuple(converted)
docs: * What you can do
          - it normalizes string types into str