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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 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])))