code: def get_first_of_element(element, sub, contype=None):
      
      content = element.xpath(sub)
      return list_or_empty(content, contype)
docs: 抽取lxml.etree库中elem对象中文字
  
      Args:
          element: lxml.etree.Element
          sub: str
  
      Returns:
          elem中文字