import re
p = re.compile(r'(?<=\d)(?=(?:\d{3})+$)')
test_str = "2890191245"
tmp = [x.start() for x in re.finditer(p, test_str)]

res = [test_str[0: tmp[0]]] + [(test_str[tmp[i]: tmp[i] + 3]) for i in range(len(tmp))]

print(res)