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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 download_sifts_xml(pdb_id, outdir='', force_rerun=False):
 """Download the SIFTS file for a PDB ID. Args: pdb_id (str):
 PDB ID outdir (str):
 Output directory, current working directory if not specified. force_rerun (bool):
 If the file should be downloaded again even if it exists Returns: str: Path to downloaded file """

    baseURL = 'ftp://ftp.ebi.ac.uk/pub/databases/msd/sifts/xml/'
    filename = '{}.xml.gz'.format(pdb_id.lower())

    outfile = op.join(outdir, filename.split('.')[0] + '.sifts.xml')

    if ssbio.utils.force_rerun(flag=force_rerun, outfile=outfile):
        response = urlopen(baseURL + filename)
        with open(outfile, 'wb') as f:
            f.write(gzip.decompress(response.read()))

    return outfile