PMID to PMC API from Medline cannot convert all provided PMID about pubmed_parser HOT 6 OPEN

def parse_citation_web(pmc):
    """
    Parse citations from given PMC 
    Parameters
    ----------
    pmc: str, PMC of the document e.g. 'PMC1217341'
    Returns
    -------
    dict_out: dict, contains following keys
        pmc: Pubmed Central ID
        n_citations: number of citations for given articles
        pmc_cited: list of PMCs that cite the given PMC
    """

    link = "http://www.ncbi.nlm.nih.gov/pmc/articles/%s/citedby/" % str(pmc)
    page = requests.get(link)
    tree = html.fromstring(page.content)
    n_citations = extract_citations(tree)
    n_pages = int(n_citations/30) + 1

    pmc_cited_all = list() # all PMC cited
    citations = tree.xpath('//div[@class="rprt"]/div[@class="title"]/a/@href')[1::]
    pmc_cited = list(map(extract_pmc, citations))
    pmc_cited_all.extend(pmc_cited)
    if n_pages >= 2:
        for i in range(2, n_pages+1):
            link = "http://www.ncbi.nlm.nih.gov/pmc/articles/%s/citedby/?page=%s" % (pmc, str(i))
            page = requests.get(link)
            tree = html.fromstring(page.content)
            citations = tree.xpath('//div[@class="rprt"]/div[@class="title"]/a/@href')[1::]
            pmc_cited = list(map(extract_pmc, citations))
            pmc_cited_all.extend(pmc_cited)
    pmc_cited_all = [p for p in pmc_cited_all if p is not pmc]
    dict_out = {'n_citations': n_citations,
                'pmc': pmc,
                'pmc_cited': pmc_cited_all}
    return dict_out