I don't know how fast this is (Python 2.x):
>>> from itertools import groupby
>>> t = 'si_pos_99_rep_1_0.ita'
>>> tuple(int("".join(g)) if h else "".join(g) for h,g in groupby(t, str.isdigit))
('si_pos_', 99, '_rep_', 1, '_', 0, '.ita')
It doesn't work with unicode strings.
Bye,
bearophile