Your expected result does not contain all possible permutations, so not sure this is what you want, or you missed some. But to get all possible permutations of a list of different lengths, you can do as follows:
from itertools import permutations
a_list = [1,2,3]
perm_list = [p for l in range(1, len(a_list)+1) for p in permutations(a_list,l)]
print(perm_list)
The result is:
[(1,), (2,), (3,), (1, 2), (1, 3), (2, 1), (2, 3), (3, 1), (3, 2), (1, 2, 3), (1, 3, 2), (2, 1, 3), (2, 3, 1), (3, 1, 2), (3, 2, 1)]
If the input list is large though, probably it would be better to use generator expression, e.g.
perm_list_gen = (p for l in range(1, len(a_list)+1) for p in permutations(a_list,l))
print(perm_list_gen)
#prints: <generator object <genexpr> at 0x7f176bbd88b8>
And than just go one by one, instead of everything at once:
for perm in perm_list_gen:
print(perm)