tf.contrib.distributions.DirichletMultinomial.prob(value, name='prob')
Probability density/mass function (depending on is_continuous).
Additional documentation from DirichletMultinomial:
For each batch of counts [n_1,...,n_k], P[counts] is the probability that after sampling n draws from this Dirichlet Multinomial distribution, the number of draws falling in class j is n_j. Note that different sequences of draws can result in the same counts, thus the probability includes a combinatorial coeff