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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 _bell(self):
        u'''ring the bell if requested.'''
        if self.bell_style == u'none':
            pass
        elif self.bell_style == u'visible':
            raise NotImplementedError(u"Bellstyle visible is not implemented yet.")
        elif self.bell_style == u'audible':
            self.console.bell()
        else:
            raise ReadlineError(u"Bellstyle %s unknown."%self.bell_style)