python去除列表中重复的元素

#python列表去除重复的元素

#1
l1 = ['b','c','d','c','a','a']
l2 = list(set(l1))
print l2

#2
l2.sort(key=l1.index)
print l2  #保持原来的顺序

#3
l1 = ['b','c','d','c','a','a']
l2 = []
for i in l1:  #[l2.append(i) for i in l1 if not i in l2]
if not i in l2:
l2.append(i)
print l2    <span style="font-family: Arial, Helvetica, sans-serif;">#保持原来的顺序</span>