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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 _write_cert_to_database(ca_name, cert, cacert_path=None, status='V'):
    '''
    write out the index.txt database file in the appropriate directory to
    track certificates

    ca_name
        name of the CA
    cert
        certificate to be recorded
    '''
    set_ca_path(cacert_path)
    ca_dir = '{0}/{1}'.format(cert_base_path(), ca_name)
    index_file, expire_date, serial_number, subject = _get_basic_info(
        ca_name,
        cert,
        ca_dir)

    index_data = '{0}\t{1}\t\t{2}\tunknown\t{3}'.format(
        status,
        expire_date,
        serial_number,
        subject
    )

    with salt.utils.files.fopen(index_file, 'a+') as ofile:
        ofile.write(salt.utils.stringutils.to_str(index_data))