return P[nonT -> tok], 
        e.g., P[ W3 -> 'abc']

def tokprob(self, tok, nonT):
        """
        return P[nonT -> tok], 
        e.g., P[ W3 -> 'abc']
        """

        p = self._T.get(tok, 0) / float(self._T.get(nonT, 1))
        if not p:
            p = MIN_PROB
        return p