抽取lxml.etree库中elem对象中文字

    Args:
        element: lxml.etree.Element
        sub: str

    Returns:
        elem中文字

def get_first_of_element(element, sub, contype=None):
    """抽取lxml.etree库中elem对象中文字

    Args:
        element: lxml.etree.Element
        sub: str

    Returns:
        elem中文字
    """
    content = element.xpath(sub)
    return list_or_empty(content, contype)