How to use the onelogin.saml2.utils.OneLogin_Saml2_Utils.element_text function in onelogin

def _parse_certificates(self, certificate_nodes):
        """Parses XML nodes containing X.509 certificates into a list of strings

        :param certificate_nodes: List of XML nodes containing X.509 certificates
        :type certificate_nodes: List[defusedxml.lxml.RestrictedElement]

        :return: List of string containing X.509 certificates
        :rtype: List[string]

        :raise: MetadataParsingError
        """
        certificates = []

        try:
            for certificate_node in certificate_nodes:
                certificates.append(''.join(OneLogin_Saml2_Utils.element_text(certificate_node).split()))
        except XMLSyntaxError as exception:
            raise SAMLMetadataParsingError(inner_exception=exception)

        return certificates

if len(slo_nodes) > 0:
                    idp_slo_url = slo_nodes[0].get('Location', None)

                signing_nodes = OneLogin_Saml2_Utils.query(idp_descriptor_node, "./md:KeyDescriptor[not(contains(@use, 'encryption'))]/ds:KeyInfo/ds:X509Data/ds:X509Certificate")
                encryption_nodes = OneLogin_Saml2_Utils.query(idp_descriptor_node, "./md:KeyDescriptor[not(contains(@use, 'signing'))]/ds:KeyInfo/ds:X509Data/ds:X509Certificate")

                if len(signing_nodes) > 0 or len(encryption_nodes) > 0:
                    certs = {}
                    if len(signing_nodes) > 0:
                        certs['signing'] = []
                        for cert_node in signing_nodes:
                            certs['signing'].append(''.join(OneLogin_Saml2_Utils.element_text(cert_node).split()))
                    if len(encryption_nodes) > 0:
                        certs['encryption'] = []
                        for cert_node in encryption_nodes:
                            certs['encryption'].append(''.join(OneLogin_Saml2_Utils.element_text(cert_node).split()))

                data['idp'] = {}

                if idp_entity_id is not None:
                    data['idp']['entityId'] = idp_entity_id

                if idp_sso_url is not None:
                    data['idp']['singleSignOnService'] = {}
                    data['idp']['singleSignOnService']['url'] = idp_sso_url
                    data['idp']['singleSignOnService']['binding'] = required_sso_binding

                if idp_slo_url is not None:
                    data['idp']['singleLogoutService'] = {}
                    data['idp']['singleLogoutService']['url'] = idp_slo_url
                    data['idp']['singleLogoutService']['binding'] = required_slo_binding

if len(encrypted_data_nodes) == 1:
                encrypted_data = encrypted_data_nodes[0]
                name_id = OneLogin_Saml2_Utils.decrypt_element(encrypted_data, key)
        else:
            entries = OneLogin_Saml2_Utils.query(elem, '/samlp:LogoutRequest/saml:NameID')
            if len(entries) == 1:
                name_id = entries[0]

        if name_id is None:
            raise OneLogin_Saml2_ValidationError(
                'NameID not found in the Logout Request',
                OneLogin_Saml2_ValidationError.NO_NAMEID
            )

        name_id_data = {
            'Value': OneLogin_Saml2_Utils.element_text(name_id)
        }
        for attr in ['Format', 'SPNameQualifier', 'NameQualifier']:
            if attr in name_id.attrib.keys():
                name_id_data[attr] = name_id.attrib[attr]

        return name_id_data

def get_issuer(self):
        """
        Gets the Issuer of the Logout Response Message
        :return: The Issuer
        :rtype: string
        """
        issuer = None
        issuer_nodes = self.__query('/samlp:LogoutResponse/saml:Issuer')
        if len(issuer_nodes) == 1:
            issuer = OneLogin_Saml2_Utils.element_text(issuer_nodes[0])
        return issuer

is_strict = self.__settings.is_strict()
        want_nameid = self.__settings.get_security_data().get('wantNameId', True)
        if nameid is None:
            if is_strict and want_nameid:
                raise OneLogin_Saml2_ValidationError(
                    'NameID not found in the assertion of the Response',
                    OneLogin_Saml2_ValidationError.NO_NAMEID
                )
        else:
            if is_strict and want_nameid and not OneLogin_Saml2_Utils.element_text(nameid):
                raise OneLogin_Saml2_ValidationError(
                    'An empty NameID value found',
                    OneLogin_Saml2_ValidationError.EMPTY_NAMEID
                )

            nameid_data = {'Value': OneLogin_Saml2_Utils.element_text(nameid)}
            for attr in ['Format', 'SPNameQualifier', 'NameQualifier']:
                value = nameid.get(attr, None)
                if value:
                    if is_strict and attr == 'SPNameQualifier':
                        sp_data = self.__settings.get_sp_data()
                        sp_entity_id = sp_data.get('entityId', '')
                        if sp_entity_id != value:
                            raise OneLogin_Saml2_ValidationError(
                                'The SPNameQualifier value mistmatch the SP entityID value.',
                                OneLogin_Saml2_ValidationError.SP_NAME_QUALIFIER_NAME_MISMATCH
                            )

                    nameid_data[attr] = value
        return nameid_data

nameid = OneLogin_Saml2_Utils.decrypt_element(encrypted_data, key)
        else:
            nameid_nodes = self.__query_assertion('/saml:Subject/saml:NameID')
            if nameid_nodes:
                nameid = nameid_nodes[0]

        is_strict = self.__settings.is_strict()
        want_nameid = self.__settings.get_security_data().get('wantNameId', True)
        if nameid is None:
            if is_strict and want_nameid:
                raise OneLogin_Saml2_ValidationError(
                    'NameID not found in the assertion of the Response',
                    OneLogin_Saml2_ValidationError.NO_NAMEID
                )
        else:
            if is_strict and want_nameid and not OneLogin_Saml2_Utils.element_text(nameid):
                raise OneLogin_Saml2_ValidationError(
                    'An empty NameID value found',
                    OneLogin_Saml2_ValidationError.EMPTY_NAMEID
                )

            nameid_data = {'Value': OneLogin_Saml2_Utils.element_text(nameid)}
            for attr in ['Format', 'SPNameQualifier', 'NameQualifier']:
                value = nameid.get(attr, None)
                if value:
                    if is_strict and attr == 'SPNameQualifier':
                        sp_data = self.__settings.get_sp_data()
                        sp_entity_id = sp_data.get('entityId', '')
                        if sp_entity_id != value:
                            raise OneLogin_Saml2_ValidationError(
                                'The SPNameQualifier value mistmatch the SP entityID value.',
                                OneLogin_Saml2_ValidationError.SP_NAME_QUALIFIER_NAME_MISMATCH

def get_audiences(self):
        """
        Gets the audiences

        :returns: The valid audiences for the SAML Response
        :rtype: list
        """
        audience_nodes = self.__query_assertion('/saml:Conditions/saml:AudienceRestriction/saml:Audience')
        return [OneLogin_Saml2_Utils.element_text(node) for node in audience_nodes if OneLogin_Saml2_Utils.element_text(node) is not None]

:param request: Logout Request Message
        :type request: string|DOMDocument
        :return: The Issuer
        :rtype: string
        """
        if isinstance(request, etree._Element):
            elem = request
        else:
            if isinstance(request, Document):
                request = request.toxml()
            elem = fromstring(request, forbid_dtd=True)

        issuer = None
        issuer_nodes = OneLogin_Saml2_Utils.query(elem, '/samlp:LogoutRequest/saml:Issuer')
        if len(issuer_nodes) == 1:
            issuer = OneLogin_Saml2_Utils.element_text(issuer_nodes[0])
        return issuer

:param request: Logout Request Message
        :type request: string|DOMDocument
        :return: The SessionIndex value
        :rtype: list
        """
        if isinstance(request, etree._Element):
            elem = request
        else:
            if isinstance(request, Document):
                request = request.toxml()
            elem = fromstring(request, forbid_dtd=True)

        session_indexes = []
        session_index_nodes = OneLogin_Saml2_Utils.query(elem, '/samlp:LogoutRequest/samlp:SessionIndex')
        for session_index_node in session_index_nodes:
            session_indexes.append(OneLogin_Saml2_Utils.element_text(session_index_node))
        return session_indexes