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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 setup(config=None, logfile=None):
 """This method sets up the default configuration of the logger. Once this method is called all subsequent instances Logger instances will inherit this configuration."""


        if config is None:
            configpath = os.path.join(fermipy.PACKAGE_ROOT, 'config',
                                      'logging.yaml')
            with open(configpath, 'r') as f:
                config = yaml.load(f)

        # Update configuration
        if logfile:
            for name, h in config['handlers'].items():
                if 'file_handler' in name:
                    config['handlers'][name]['filename'] = logfile

        logging.config.dictConfig(config)