code: def define_selector(by, value, el_class):
      
      el = el_class
      selector = by
      if isinstance(value, six.string_types):
          selector = (by, value)
      elif value is not None:
          el = value
  
      if el is None:
          el = elements.PageElement
  
      return el, selector
docs: :param by:
      :param value:
      :param el_class:
      :rtype: tuple[type, str|tuple[str, str]]
      :return: