output = inputstr.rsplit('.', 1)[0]
output = inputstr.rpartition('.')[0]
>>> 'test.test1.test2'.rsplit('.', 1)[0]
'test.test1'
>>> 'test.test1.test2'.rpartition('.')[0]
'test.test1'
>>> 'test.test3.test4'.rsplit('.', 1)[0]
'test.test3'
>>> 'test.test3.test4'.rpartition('.')[0]
'test.test3'
>>> from timeit import timeit
>>> timeit("s.rsplit('.', 1)[0]", "s = 'test.test1.test2'")
0.5848979949951172
>>> timeit("s.rpartition('.')[0]", "s = 'test.test1.test2'")
0.27417516708374023