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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_article_xml(pubmed_id):
 """Get the XML metadata for a single article from the Pubmed database. """

    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