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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 find_config(config_path: str) -> str: """ Derive configuration file path from the given path and check its existence. The given path is expected to be either 1. path to the file 2. path to a dir, in such case the path is joined with ``CXF_CONFIG_FILE`` :param config_path: path to the configuration file or its parent directory :return: validated configuration file path """

    if path.isdir(config_path):  # dir specified instead of config file
        config_path = path.join(config_path, CXF_CONFIG_FILE)
    assert path.exists(config_path), '`{}` does not exist'.format(config_path)
    return config_path