How to use the biblib.util.xmletree.get_element_attribute_as_boolean function in biblib

def get_rml_phones(rml):
    """ phone -> phones """
    result = {}
    rml_phones = rml.findall(xmletree.prefixtag("rml", "phone"))
    if rml_phones is not None:
        phones = []
        for rml_phone in rml_phones:
            if rml_phone is not None:
                # @preferred -> preferred
                preferred = xmletree.get_element_attribute_as_boolean(rml_phone, "preferred")
                # @relationType -> relation_type
                relation_type = rml_phone.get("relationType")
                # @type -> phone_type
                phone_type = rml_phone.get("type")
                # @visible -> visible
                visible = xmletree.get_element_attribute_as_boolean(rml_phone, "visible")
                # formatted -> formatted
                rml_formatted = rml_phone.find(xmletree.prefixtag("rml", "formatted"))
                formatted = xmletree.get_element_text(rml_formatted)

                phone = metajson_service.create_phone(formatted, phone_type, preferred, relation_type, visible)
                if phone:
                    phones.append(phone)
        if phones:
            result["phones"] = phones
    return result

def get_rml_uris(rml):
    """ uri -> urls """
    result = {}
    rml_uris = rml.findall(xmletree.prefixtag("rml", "uri"))
    if rml_uris is not None:
        urls = []
        for rml_uri in rml_uris:
            if rml_uri is not None:
                preferred = xmletree.get_element_attribute_as_boolean(rml_uri, "preferred")
                relation_type = rml_uri.get("relationType")
                visible = xmletree.get_element_attribute_as_boolean(rml_uri, "visible")
                value = xmletree.get_element_text(rml_uri)

                url = metajson_service.create_url(value, preferred, relation_type, None, None, visible)
                if url:
                    urls.append(url)
        if urls:
            result["urls"] = urls
    return result

def get_rml_uris(rml):
    """ uri -> urls """
    result = {}
    rml_uris = rml.findall(xmletree.prefixtag("rml", "uri"))
    if rml_uris is not None:
        urls = []
        for rml_uri in rml_uris:
            if rml_uri is not None:
                preferred = xmletree.get_element_attribute_as_boolean(rml_uri, "preferred")
                relation_type = rml_uri.get("relationType")
                visible = xmletree.get_element_attribute_as_boolean(rml_uri, "visible")
                value = xmletree.get_element_text(rml_uri)

                url = metajson_service.create_url(value, preferred, relation_type, None, None, visible)
                if url:
                    urls.append(url)
        if urls:
            result["urls"] = urls
    return result

locality_city_town = xmletree.get_element_text(rml_address.find(xmletree.prefixtag("rml", "localityCityTown")))

                # post_code -> post_code
                post_code = xmletree.get_element_text(rml_address.find(xmletree.prefixtag("rml", "postCode")))

                # @preferred -> preferred
                preferred = xmletree.get_element_attribute_as_boolean(rml_address, "preferred")

                # @relationType -> relation_type
                relation_type = rml_address.get("relationType")

                # street -> street
                street = xmletree.get_element_text(rml_address.find(xmletree.prefixtag("rml", "street")))

                # @visible -> visible
                visible = xmletree.get_element_attribute_as_boolean(rml_address, "visible")

                # address -> addresses[i]
                address = metajson_service.create_address(street, post_code, locality_city_town, country, preferred, relation_type, visible)

                if address:
                    addresses.append(address)
        if addresses:
            result["addresses"] = addresses
    return result

date_end = get_rml_element_text(rml_affiliation, "dateEnd")

                # description -> descriptions
                descriptions = get_rml_textlangs_as_list(rml_affiliation, "description")

                # identifier -> agent.rec_id
                identifiers = get_rml_identifiers(rml_affiliation)
                rec_id = None
                if "rec_id" in identifiers and identifiers["rec_id"]:
                    rec_id = identifiers["rec_id"]

                # name -> agent.name
                name = get_rml_element_text(rml_affiliation, "name")

                # @preferred -> preferred
                preferred = xmletree.get_element_attribute_as_boolean(rml_affiliation, "preferred")

                # relationType -> role
                role = get_rml_element_text(rml_affiliation, "relationType")

                affiliation = metajson_service.create_affiliation(rec_id, name, role, date_begin, date_end, preferred, descriptions)
                if affiliation is not None:
                    affiliations.append(affiliation)
        if affiliations:
            result["affiliations"] = affiliations
    return result

def get_rml_emails(rml):
    """ email -> emails """
    result = {}
    rml_emails = rml.findall(xmletree.prefixtag("rml", "email"))
    if rml_emails is not None:
        emails = []
        for rml_email in rml_emails:
            if rml_email is not None:
                # @preferred -> preferred
                preferred = xmletree.get_element_attribute_as_boolean(rml_email, "preferred")

                # @relationType -> relation_type
                relation_type = rml_email.get("relationType")

                # @visible -> visible
                visible = xmletree.get_element_attribute_as_boolean(rml_email, "visible")

                # value
                value = xmletree.get_element_text(rml_email)

                email = metajson_service.create_email(value, preferred, relation_type, visible)
                if email:
                    emails.append(email)
        if emails:
            result["emails"] = emails
    return result