def tostring(element):  # pylint:disable=unused-variable
        """Serialize an element and its child nodes to a string"""
        rv = []
        filter = _ihatexml.InfosetFilter()

        def serializeElement(element):
            if isinstance(element, ElementTree.ElementTree):
                element = element.getroot()

            if element.tag == "<!DOCTYPE>":
                if element.get("publicId") or element.get("systemId"):
                    publicId = element.get("publicId") or ""
                    systemId = element.get("systemId") or ""
                    rv.append("""<!DOCTYPE %s PUBLIC "%s" "%s">""" %
                              (element.text, publicId, systemId))
                else:
                    rv.append("<!DOCTYPE %s>" % (element.text,))
            elif element.tag == "DOCUMENT_ROOT":
                if element.text is not None:
                    rv.append(element.text)
                if element.tail is not None:
                    raise TypeError("Document node cannot have tail")
                if hasattr(element, "attrib") and len(element.attrib):
                    raise TypeError("Document node cannot have attributes")

                for child in element:
                    serializeElement(child)

            elif element.tag == ElementTreeCommentType:
                rv.append("<!--%s-->" % (element.text,))
            else:
                # This is assumed to be an ordinary element
                if not element.attrib:
                    rv.append("<%s>" % (filter.fromXmlName(element.tag),))
                else:
                    attr = " ".join(["%s=\"%s\"" % (
                        filter.fromXmlName(name), value)
                        for name, value in element.attrib.items()])
                    rv.append("<%s %s>" % (element.tag, attr))
                if element.text:
                    rv.append(element.text)

                for child in element:
                    serializeElement(child)

                rv.append("</%s>" % (element.tag,))

            if element.tail:
                rv.append(element.tail)

        serializeElement(element)

        return "".join(rv)
Serialize an element and its child nodes to a string
product/gradle-plugin/src/main/python/pip/_vendor/html5lib/treebuilders/etree.py