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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 __create_event(self):
 """ Create an SQLAlchemy event listening the 'set' in a particular column. :rtype : object """

        if not event.contains(self.field, 'set', self.__validate):
            event.listen(self.field, 'set', self.__validate, retval=True)