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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_num_bioassemblies(pdb_id, cache=False, outdir=None, force_rerun=False):
 """Check if there are bioassemblies using the PDB REST API, and if there are, get the number of bioassemblies available. See: https://www.rcsb.org/pages/webservices/rest, section 'List biological assemblies' Not all PDB entries have biological assemblies available and some have multiple. Details that are necessary to recreate a biological assembly from the asymmetric unit can be accessed from the following requests. - Number of biological assemblies associated with a PDB entry - Access the transformation information needed to generate a biological assembly (nr=0 will return information for the asymmetric unit, nr=1 will return information for the first assembly, etc.) A query of https://www.rcsb.org/pdb/rest/bioassembly/nrbioassemblies?structureId=1hv4 returns this:: <nrBioAssemblies structureId="1HV4" hasAssemblies="true" count="2"/> Args: pdb_id (str):
 PDB ID cache (bool):
 If the XML file should be downloaded outdir (str):
 If cache, then specify the output directory force_rerun (bool):
 If cache, and if file exists, specify if API should be queried again """

    parser = etree.XMLParser(ns_clean=True)

    if not outdir:
        outdir = os.getcwd()
    outfile = op.join(outdir, '{}_nrbiomols.xml'.format(pdb_id))

    if ssbio.utils.force_rerun(force_rerun, outfile):
        page = 'https://www.rcsb.org/pdb/rest/bioassembly/nrbioassemblies?structureId={}'.format(pdb_id)
        req = requests.get(page)

        if req.status_code == 200:
            response = req.text

            # Save the XML file
            if cache:
                with open(outfile, 'w') as f:
                    f.write(response)

            # Parse the XML string
            tree = etree.ElementTree(etree.fromstring(response, parser))
            log.debug('Loaded bioassembly information from REST server')
        else:
            log.error('Request timed out')
            req.raise_for_status()
    else:
        tree = etree.parse(outfile, parser)
        log.debug('{}: Loaded existing XML results'.format(outfile))

    r = tree.getroot()
    has_biomols = r.get('hasAssemblies')
    if has_biomols == 'true':
        has_biomols = True
    else:
        has_biomols = False

    if has_biomols:
        num_biomols = r.get('count')
    else:
        num_biomols = 0

    num_biomols = int(num_biomols)
    return num_biomols