By inspecting the theano.dot source. It seems that, e1 is always set to None. The important thing is that the lines 209-210 will only be reached if neither obejct_A nor delta, or object_A nor gamma define a dot method. Could you share a more detailed example in which you add the definitions of A, t, tau, S, and object_t_change? Those variable are not defined in your snippet and maybe your problem lies somewhere in their definition.