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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_config_files():
 """Get the possible configuration files accepted by oslo.config This also includes the deprecated ones """

    # default files
    conf_files = cfg.find_config_files(project='monasca',
                                       prog='monasca-persister')
    # deprecated config files (only used if standard config files are not there)
    if len(conf_files) == 0:
        old_conf_files = cfg.find_config_files(project='monasca',
                                               prog='persister')
        if len(old_conf_files) > 0:
            LOG.warning('Found deprecated old location "{}" '
                        'of main configuration file'.format(old_conf_files))
            conf_files += old_conf_files
    return conf_files