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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 prettify_json_file(file_list):
 """ prettify JSON testcase format """

    for json_file in set(file_list):
        if not json_file.endswith(".json"):
            logger.log_warning("Only JSON file format can be prettified, skip: {}".format(json_file))
            continue

        logger.color_print("Start to prettify JSON file: {}".format(json_file), "GREEN")

        dir_path = os.path.dirname(json_file)
        file_name, file_suffix = os.path.splitext(os.path.basename(json_file))
        outfile = os.path.join(dir_path, "{}.pretty.json".format(file_name))

        with io.open(json_file, 'r', encoding='utf-8') as stream:
            try:
                obj = json.load(stream)
            except ValueError as e:
                raise SystemExit(e)

        with io.open(outfile, 'w', encoding='utf-8') as out:
            json.dump(obj, out, indent=4, separators=(',', ': '))
            out.write('\n')

        print("success: {}".format(outfile))