Here is a trivial example that works in 0.8.3 but not in 0.9.1: import ChiantiPy.core as ch t = 10.*(5.8 + 0.05*np.arange(21.)) o3 = ch.ion('o_8', temperature=t) o3.recombRate() o3 = ch.ion('o_9', temperature=t) o3.recombRate()