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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 uniprot_ec(uniprot_id):
 """Retrieve the EC number annotation for a UniProt ID. Args: uniprot_id: Valid UniProt ID Returns: """

    r = requests.post('http://www.uniprot.org/uniprot/?query=%s&columns=ec&format=tab' % uniprot_id)
    ec = r.content.decode('utf-8').splitlines()[1]

    if len(ec) == 0:
        ec = None

    return ec