code: def get_article_xml(pubmed_id):
      
      if pubmed_id.upper().startswith('PMID'):
          pubmed_id = pubmed_id[4:]
      params = {'db': 'pubmed',
                'retmode': 'xml',
                'id': pubmed_id}
      tree = send_request(pubmed_fetch, params)
      if tree is None:
          return None
      article = tree.find('PubmedArticle/MedlineCitation/Article')
      return article
docs: Get the XML metadata for a single article from the Pubmed database.