How to use the owslib.etree.etree.tostring function in OWSLib

("STATISTICS", "MEAN"),
              ("STATISTICS", "MINIMUM"),
              ("STATISTICS", "MAXIMUM"),
              ("STATISTICS", "WEIGHT_SUM"),
              ("STATISTICS", "VARIANCE"),
              ("STATISTICS", "STD_DEV"),
              ("STATISTICS", "COUNT"),
              ("GROUP_BY", "STATISTIC"),
              ("SUMMARIZE_TIMESTEP", "false"),
              ("SUMMARIZE_FEATURE_ATTRIBUTE", "false"),
              ("FEATURE_COLLECTION", featureCollection)]
    output = "OUTPUT"
    # build XML request for WPS process execution
    execution = WPSExecution()
    requestElement = execution.buildRequest(processid, inputs, output=[(output, True)])
    request = etree.tostring(requestElement)
    # Compare to cached XML request
    _request = open(resource_file('wps_USGSExecuteRequest3.xml'), 'rb').read()
    assert compare_xml(request, _request) is True

("STATISTICS", "MAXIMUM"),
              ("STATISTICS", "WEIGHT_SUM"),
              ("STATISTICS", "VARIANCE"),
              ("STATISTICS", "STD_DEV"),
              ("STATISTICS", "COUNT"),
              ("GROUP_BY", "STATISTIC"),
              ("SUMMARIZE_TIMESTEP", "true"),
              ("SUMMARIZE_FEATURE_ATTRIBUTE", "true"),
              ("FEATURE_COLLECTION", featureCollection)
              ]
    output = "OUTPUT"

    # build XML request for WPS process execution
    execution = WPSExecution()
    requestElement = execution.buildRequest(processid, inputs, output=[(output, True)])
    request = etree.tostring(requestElement)

    # Compare to cached XML request
    _request = open(resource_file('wps_USGSExecuteRequest2.xml'), 'rb').read()
    assert compare_xml(request, _request) is True

def __init__(self, record):

        if hasattr(record, 'getroot'):  # standalone document
            self.xml = etree.tostring(record.getroot())
        else:  # part of a larger document
            self.xml = etree.tostring(record)

        # check to see if Dublin Core record comes from
        # rdf:RDF/rdf:Description container
        # (child content model is identical)
        self.rdf = False
        rdf = record.find(util.nspath_eval('rdf:Description', namespaces))
        if rdf is not None:
            self.rdf = True
            record = rdf

        # some CSWs return records with multiple identifiers based on 
        # different schemes.  Use the first dc:identifier value to set
        # self.identifier, and set self.identifiers as a list of dicts
        val = record.find(util.nspath_eval('dc:identifier', namespaces))
        self.identifier = util.testXMLValue(val)

- dname: the value of the Parameter or Property to query
        - dtype: whether to query a parameter (parameter) or property (property)

        """

        # construct request
        dtypename = 'ParameterName'
        node0 = etree.Element(util.nspath_eval('csw:GetDomain', namespaces))
        node0.set('service', self.service)
        node0.set('version', self.version)
        node0.set(util.nspath_eval('xsi:schemaLocation', namespaces), schema_location)
        if dtype == 'property':
            dtypename = 'PropertyName'
        etree.SubElement(node0, util.nspath_eval('csw:%s' % dtypename, namespaces)).text = dname
        self.request = util.xml2string(etree.tostring(node0))

        self._invoke()

        if self.exceptionreport is None:
            self.results = {}

            val = self._exml.find(util.nspath_eval('csw:DomainValues', namespaces)).attrib.get('type')
            self.results['type'] = util.testXMLValue(val, True)

            val = self._exml.find(util.nspath_eval('csw:DomainValues/csw:%s' % dtypename, namespaces))
            self.results[dtype] = util.testXMLValue(val)

            # get the list of values associated with the Domain
            self.results['values'] = []

            for f in self._exml.findall(util.nspath_eval('csw:DomainValues/csw:ListOfValues/csw:Value', namespaces)):

def getServiceXML(self):
        xml = None
        if self._capabilities is not None:
            xml = etree.tostring(self._capabilities)
        return xml

def __init__(self, md):
        if hasattr(md, 'getroot'):  # standalone document
            self.xml = etree.tostring(md.getroot())
        else:  # part of a larger document
            self.xml = etree.tostring(md)

        self.idinfo = Idinfo(md)
        self.eainfo = Eainfo(md)
        self.distinfo = Distinfo(md)
        self.metainfo = Metainfo(md)

        if self.idinfo.datasetid:
            self.identifier = self.idinfo.datasetid

reader = WPSExecuteReader(verbose=self.verbose)
        if response is None:
            # override status location
            if url is not None:
                self.statusLocation = url
            log.info('\nChecking execution status... (location=%s)' % self.statusLocation)
            try:
                response = reader.readFromUrl(  self.statusLocation, username=self.username, password=self.password, headers=self.headers, verify=self.verify, cert=self.cert)
            except Exception as err:
                log.error( "Could not read status document using url " + str(self.statusLocation) + ": " + str(err) + "\n" + traceback.format_exc() )
        else:
            response = reader.readFromString(response)

        # store latest response
        try:
            xml = etree.tostring(response)
        except Exception:
            log.error("Could not parse XML response: " + str(response) )
        else:
            self.response = xml
#            log.info(self.response)

            self.parseResponse(response)

            # sleep given number of seconds
            if self.isComplete() is False:
                log.info('Sleeping %d seconds...' % sleepSecs)
                sleep(sleepSecs)

- xml_declaration (optional): whether to include xml declaration

    """

    output = None

    if encoding is None:
        encoding = "ISO-8859-1"

    if etree.__name__ == 'lxml.etree':
        if xml_declaration:
            if encoding in ['unicode', 'utf-8']:
                output = '\n{}'.format(
                    etree.tostring(element, encoding='unicode'))
            else:
                output = etree.tostring(element, encoding=encoding, xml_declaration=True)
        else:
            output = etree.tostring(element)
    else:
        if xml_declaration:
            output = '\n{}'.format(
                encoding, etree.tostring(element, encoding=encoding))
        else:
            output = etree.tostring(element)

    return output

if encoding is None:
        encoding = "ISO-8859-1"

    if etree.__name__ == 'lxml.etree':
        if xml_declaration:
            if encoding in ['unicode', 'utf-8']:
                output = '\n{}'.format(
                    etree.tostring(element, encoding='unicode'))
            else:
                output = etree.tostring(element, encoding=encoding, xml_declaration=True)
        else:
            output = etree.tostring(element)
    else:
        if xml_declaration:
            output = '\n{}'.format(
                encoding, etree.tostring(element, encoding=encoding))
        else:
            output = etree.tostring(element)

    return output

if url is not None:
                self.statusLocation = url
            log.info('\nChecking execution status... (location=%s)' %
                     self.statusLocation)
            try:
                response = reader.readFromUrl(
                    self.statusLocation, username=self.username, password=self.password,
                    headers=self.headers, verify=self.verify, cert=self.cert)
            except Exception:
                log.error("Could not read status document.")
        else:
            response = reader.readFromString(response)

        # store latest response
        try:
            xml = etree.tostring(response)
        except Exception:
            log.error("Could not parse XML response.")
        else:
            self.response = xml
            log.debug(self.response)

            self.parseResponse(response)

            # sleep given number of seconds
            if self.isComplete() is False:
                log.info('Sleeping %d seconds...' % sleepSecs)
                sleep(sleepSecs)