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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 _update_from_file(self, filename):
 """ Helper method to update an existing configuration with the values from a file. Loads a configuration file and replaces all values in the existing configuration dictionary with the values from the file. Args: filename (str):
 The path and name to the configuration file. """

        if os.path.exists(filename):
            try:
                with open(filename, 'r') as config_file:
                    yaml_dict = yaml.safe_load(config_file.read())
                    if yaml_dict is not None:
                        self._update_dict(self._config, yaml_dict)
            except IsADirectoryError:
                raise ConfigLoadError(
                    'The specified configuration file is a directory not a file')
        else:
            raise ConfigLoadError('The config file {} does not exist'.format(filename))