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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 _chk_docopt_exit(self, args, exp_letters):
 """Check if docopt exit was for an unknown argument."""

        if args is None:
            args = sys.argv[1:]
        keys_all = self.exp_keys.union(self.exp_elems)
        if exp_letters:
            keys_all |= exp_letters
        unknown_args = self._chk_docunknown(args, keys_all)
        if unknown_args:
            raise RuntimeError("{USAGE}\n    **FATAL: UNKNOWN ARGS: {UNK}".format(
                USAGE=self.doc, UNK=" ".join(unknown_args)))