def METHOD_NAME(self, reaction, T):
    """
    Return the diffusion factor of the specified reaction
    This is the ratio of k_eff to k_intrinsic, which is between 0 and 1.
    It is 1.0 if diffusion has no effect.
    """
    return self.get_effective_rate(reaction, T) / reaction.kinetics.get_rate_coefficient(T, P=0)