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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 merge_config( config: Mapping[str, Any], override_config: Mapping[str, Any] = None, override_config_fn: str = None, ) -> Mapping[str, Any]: """Override config with additional configuration in override_config or override_config_fn Used in script to merge CLI options with Config Args: config: original configuration override_config: new configuration to override/extend current config override_config_fn: new configuration filename as YAML file """


    if override_config_fn:
        with open(override_config_fn, "r") as f:
            override_config = yaml.load(f, Loader=yaml.SafeLoader)

    if not override_config:
        log.info("Missing override_config")

    return functools.reduce(rec_merge, (config, override_config))