Generate all the possible sublists of a list

generate_sublists.py

def sublists(symps):
# sample input [1,2,3] Ex Output [[1],[2],[3],[1,2],[2,3],[1,3],[1,2,3]]
        length = len(symps)
        i = 0
        poss = []
        while i < length:
                temp = []
                size = length - i
                temp = [sublist for sublist in (symps[x:x+size] for x in range(len(symps) - size + 1))]
                i = i +1
                #for l in temp:
                #poss.append(temp)
                for l in temp:
                        poss.append(l)
        return poss
print sublists([1,2,3])