import scriptcontext as sc

if not sc.sticky.get('triplet'):
    sc.sticky['triplet'] = (None,(None, None, None))

xyz = (x, y, z)
for i, (u, v) in enumerate(zip(xyz, sc.sticky['triplet'][1])):
    if u != v:
        sc.sticky['triplet'] = (i, xyz)
        break

a = sc.sticky['triplet'][0]