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
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.