def permutations(xs):
ac = [[]]
for x in xs:
ac_new = []
for ts in ac:
for n in range(0,ts.__len__()+1):
new_ts = ts[:] #(shallow) copy of ts
new_ts.insert(n,x)
ac_new.append(new_ts)
ac=ac_new
return ac
print(permutations([1,2,3,4]))