returns the propagation bit of a text value

def getPropagationBit(self, t, p):
        '''
        returns the propagation bit of a text value
        '''
        try:
            return self.validPropagations[t][p]['BITS']
        except KeyError:
            raise CommandExecutionError((
                'No propagation type of "{0}".  It should be one of the following:  {1}'
                ).format(p, ', '.join(self.validPropagations[t])))