How to use the wikidataintegrator.wdi_core.WDString function in wikidataintegrator

for n, author in enumerate(self.meta['authors'], 1):
            if ordinals is not None and n in ordinals:
                continue
            series_ordinal = wdi_core.WDString(str(n), self.PROPS['series ordinal'], is_qualifier=True)
            if author in self.meta['author_orcid']:
                if self.meta['author_qid'][author]:
                    s.append(wdi_core.WDItemID(self.meta['author_qid'][author], self.PROPS['author'],
                                               references=[self.reference], qualifiers=[series_ordinal]))
                else:
                    msg = "No Author found for author: {}, orcid: {}".format(author, self.meta['author_orcid'][author])
                    self.warnings.append(msg)
                    print(msg)
                    s.append(wdi_core.WDString(author, self.PROPS['author name string'],
                                               references=[self.reference], qualifiers=[series_ordinal]))
            elif author:
                s.append(wdi_core.WDString(author, self.PROPS['author name string'],
                                           references=[self.reference], qualifiers=[series_ordinal]))
        return s

:return:
        """
        s = []
        for n, author in enumerate(self.meta['authors'], 1):
            if ordinals is not None and n in ordinals:
                continue
            series_ordinal = wdi_core.WDString(str(n), self.PROPS['series ordinal'], is_qualifier=True)
            if author in self.meta['author_orcid']:
                if self.meta['author_qid'][author]:
                    s.append(wdi_core.WDItemID(self.meta['author_qid'][author], self.PROPS['author'],
                                               references=[self.reference], qualifiers=[series_ordinal]))
                else:
                    msg = "No Author found for author: {}, orcid: {}".format(author, self.meta['author_orcid'][author])
                    self.warnings.append(msg)
                    print(msg)
                    s.append(wdi_core.WDString(author, self.PROPS['author name string'],
                                               references=[self.reference], qualifiers=[series_ordinal]))
            elif author:
                s.append(wdi_core.WDString(author, self.PROPS['author name string'],
                                           references=[self.reference], qualifiers=[series_ordinal]))
        return s

def set_value(self, value):
        assert isinstance(value, str) or value is None, "Expected str, found {} ({})".format(type(value), value)
        self.value = value

        self.json_representation['datavalue'] = {
            'value': self.value,
            'type': 'string'
        }

        super(WDString, self).set_value(value=value)

def make_statements(self):
        s = []
        helper = self.helper
        # instance of edition
        s.append(wdi_core.WDItemID(helper.get_qid('Q3331189'), helper.get_pid("P31")))
        # edition or translation of
        s.append(wdi_core.WDItemID(self.edition_of_qid, helper.get_pid("P629")))
        # edition number
        s.append(wdi_core.WDString(self.edition, helper.get_pid("P393")))

        if self.archive_url:
            s.append(wdi_core.WDUrl(self.archive_url, helper.get_pid('P1065')))

        if self.pub_date:
            s.append(wdi_core.WDTime(self.pub_date, helper.get_pid('P577'), precision=self.date_precision))

        self.statements = s

self.make_reference()
        s = []

        ### Required statements
        for pubtype in self.meta['pubtype_qid']:
            s.append(wdi_core.WDItemID(pubtype, self.PROPS['instance of'], references=[self.reference]))
        s.append(wdi_core.WDMonolingualText(self.meta['title'], self.PROPS['title'], references=[self.reference]))
        s.append(wdi_core.WDTime(self.meta['date'], self.PROPS['publication date'], references=[self.reference]))
        s.append(wdi_core.WDItemID(self.meta['journal_wdid'], self.PROPS['published in'], references=[self.reference]))
        s.extend(self.make_author_statements(ordinals=ordinals))

        ### Optional statements
        if self.meta['pmid']:
            s.append(wdi_core.WDExternalID(self.meta['pmid'], self.PROPS['PubMed ID'], references=[self.reference]))
        if self.meta['volume']:
            s.append(wdi_core.WDString(self.meta['volume'], self.PROPS['volume'], references=[self.reference]))
        if self.meta['pages']:
            s.append(wdi_core.WDString(self.meta['pages'], self.PROPS['page(s)'], references=[self.reference]))
        if self.meta['issue']:
            s.append(wdi_core.WDString(self.meta['issue'], self.PROPS['issue'], references=[self.reference]))
        if self.meta['doi']:
            s.append(wdi_core.WDExternalID(self.meta['doi'].upper(), self.PROPS['DOI'], references=[self.reference]))
        if self.meta['pmcid']:
            s.append(wdi_core.WDExternalID(self.meta['pmcid'].replace("PMC", ""), self.PROPS['PMCID'],
                                           references=[self.reference]))

        self.statements = s

def make_statements(self):
        self.statements.append(
            wdi_core.WDItemID(self.instance_of_qid, PROPS['instance of'], references=[self.reference]))
        self.statements.append(wdi_core.WDMonolingualText(self.title, PROPS['title'], references=[self.reference]))

        if self.publication_date:
            date = self.publication_date.strftime("+%Y-%m-%dT00:00:00Z")
            self.statements.append(
                wdi_core.WDTime(date, PROPS['publication date'], references=[self.reference]))
        if self.published_in_qid:
            self.statements.append(
                wdi_core.WDItemID(self.published_in_qid, PROPS['published in'], references=[self.reference]))
        if self.volume:
            self.statements.append(wdi_core.WDString(self.volume, PROPS['volume'], references=[self.reference]))
        if self.pages:
            self.statements.append(wdi_core.WDString(self.pages, PROPS['page(s)'], references=[self.reference]))
        if self.issue:
            self.statements.append(wdi_core.WDString(self.issue, PROPS['issue'], references=[self.reference]))

wdi_core.WDItemID(self.instance_of_qid, PROPS['instance of'], references=[self.reference]))
        self.statements.append(wdi_core.WDMonolingualText(self.title, PROPS['title'], references=[self.reference]))

        if self.publication_date:
            date = self.publication_date.strftime("+%Y-%m-%dT00:00:00Z")
            self.statements.append(
                wdi_core.WDTime(date, PROPS['publication date'], references=[self.reference]))
        if self.published_in_qid:
            self.statements.append(
                wdi_core.WDItemID(self.published_in_qid, PROPS['published in'], references=[self.reference]))
        if self.volume:
            self.statements.append(wdi_core.WDString(self.volume, PROPS['volume'], references=[self.reference]))
        if self.pages:
            self.statements.append(wdi_core.WDString(self.pages, PROPS['page(s)'], references=[self.reference]))
        if self.issue:
            self.statements.append(wdi_core.WDString(self.issue, PROPS['issue'], references=[self.reference]))

for pubtype in self.meta['pubtype_qid']:
            s.append(wdi_core.WDItemID(pubtype, self.PROPS['instance of'], references=[self.reference]))
        s.append(wdi_core.WDMonolingualText(self.meta['title'], self.PROPS['title'], references=[self.reference]))
        s.append(wdi_core.WDTime(self.meta['date'], self.PROPS['publication date'], references=[self.reference]))
        s.append(wdi_core.WDItemID(self.meta['journal_wdid'], self.PROPS['published in'], references=[self.reference]))
        s.extend(self.make_author_statements(ordinals=ordinals))

        ### Optional statements
        if self.meta['pmid']:
            s.append(wdi_core.WDExternalID(self.meta['pmid'], self.PROPS['PubMed ID'], references=[self.reference]))
        if self.meta['volume']:
            s.append(wdi_core.WDString(self.meta['volume'], self.PROPS['volume'], references=[self.reference]))
        if self.meta['pages']:
            s.append(wdi_core.WDString(self.meta['pages'], self.PROPS['page(s)'], references=[self.reference]))
        if self.meta['issue']:
            s.append(wdi_core.WDString(self.meta['issue'], self.PROPS['issue'], references=[self.reference]))
        if self.meta['doi']:
            s.append(wdi_core.WDExternalID(self.meta['doi'].upper(), self.PROPS['DOI'], references=[self.reference]))
        if self.meta['pmcid']:
            s.append(wdi_core.WDExternalID(self.meta['pmcid'].replace("PMC", ""), self.PROPS['PMCID'],
                                           references=[self.reference]))

        self.statements = s

def make_reference(self):
        if not self.meta['parsed']:
            self.parse_metadata()
        if 'pmcid' in self.meta and self.meta['pmcid']:
            extid = wdi_core.WDString(value=self.meta['pmcid'], prop_nr=self.PROPS['PMCID'], is_reference=True)
            ref_url = wdi_core.WDUrl("http://europepmc.org/abstract/{}/{}".format("PMC", self.meta['pmcid']),
                                     self.PROPS['reference URL'], is_reference=True)
        elif 'pmid' in self.meta and self.meta['pmid']:
            extid = wdi_core.WDString(value=self.meta['pmid'], prop_nr=self.PROPS['PubMed ID'], is_reference=True)
            ref_url = wdi_core.WDUrl("http://europepmc.org/abstract/{}/{}".format("MED", self.meta['pmid']),
                                     self.PROPS['reference URL'], is_reference=True)
        elif 'doi' in self.meta and self.meta['doi']:
            extid = wdi_core.WDString(value=self.meta['doi'], prop_nr=self.PROPS['DOI'], is_reference=True)
            ref_url = None
        else:
            raise ValueError("ref needs a pmcid, pmid, or doi")
        stated_in = wdi_core.WDItemID(value='Q5412157', prop_nr='P248', is_reference=True)
        retrieved = wdi_core.WDTime(strftime("+%Y-%m-%dT00:00:00Z", gmtime()), prop_nr='P813', is_reference=True)
        self.reference = [stated_in, extid, retrieved]
        if ref_url:
            self.reference.append(ref_url)

def make_author_statements(self):
        # this function exists separately because if the item already exists, we don't want to touch the authors
        s = []
        for n, author in enumerate(self.authors, 1):
            series_ordinal = wdi_core.WDString(str(n), PROPS['series ordinal'], is_qualifier=True)
            if author.get("qid"):
                s.append(wdi_core.WDItemID(author['qid'], PROPS['author'],
                                           references=[self.reference], qualifiers=[series_ordinal]))
            elif author['full_name']:
                s.append(wdi_core.WDString(author['full_name'], PROPS['author name string'],
                                           references=[self.reference], qualifiers=[series_ordinal]))
        self.statements.extend(s)