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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_pmid(doc_id):
 """Get PMID from document_chembl_id Parameters doc_id : str Returns ------- pmid : str """

    url_pmid = 'https://www.ebi.ac.uk/chembl/api/data/document.json'
    params = {'document_chembl_id': doc_id}
    res = requests.get(url_pmid, params=params)
    js = res.json()
    pmid = str(js['documents'][0]['pubmed_id'])
    return pmid