【练习】（a,b）和（b,a）是相同的，如何去除（b,a）保留（a,b）

[(0, 3), (0, 11), (1, 8), (1, 9), (1, 15), (3, 0), (8, 1), (8, 9), (8, 15), (9, 1), (9, 8), (9, 15), (11, 0), (15, 1), (15, 8), (15, 9)]
里面（a,b）和（b,a）是相同的，如何去除（b,a）保留（a,b）

l1 = [(0, 3), (0, 11), (1, 8), (1, 9), (1, 15), (3, 0), (8, 1), (8, 9),
      (8, 15), (9, 1), (9, 8), (9, 15), (11, 0), (15, 1), (15, 8), (15, 9)]
new_l = []
for i in l1:
    if (i[1],i[0]) in new_l:
        pass
    else:
        new_l.append(i)
print(new_l)