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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 set_person(self, what, rep):
 """Set a person substitution. Equivalent to ``! person`` in RiveScript code. :param str what: The original text to replace. :param str rep: The text to replace it with. Set this to ``None`` to delete the substitution. """

        if rep is None:
            # Unset the variable.
            if what in self._person:
                del self._person[what]
        self._person[what] = rep