def diff_object_types_histograms(new_histo, old_histo):
    """ Returns a new histogram that is the difference of it inputs """
    all_keys = set(new_histo.keys()).union(old_histo.keys())

    dd = {k: new_histo[k] - old_histo[k] for k in all_keys if new_histo[k] - old_histo[k] != 0}
    return dd