python 去除 list 重复元素

比较容易记忆的是用内置的set   
l1 = ['b','c','d','b','c','a','a']   
l2 = list(set(l1))   
print l2   
    
还有一种据说速度更快的，没测试过两者的速度差别   
l1 = ['b','c','d','b','c','a','a']   
l2 = {}.fromkeys(l1).keys()   
print l2   
    
这两种都有个缺点，祛除重复元素后排序变了：   
['a', 'c', 'b', 'd']   
    
     
     
如果想要保持他们原来的排序：   
    
用list类的sort方法   
l1 = ['b','c','d','b','c','a','a']   
l2 = list(set(l1))   
l2.sort(key=l1.index)   
print l2   
也可以这样写   
l1 = ['b','c','d','b','c','a','a']   
l2 = sorted(set(l1),key=l1.index)   
print l2   
    
    
也可以用遍历   
l1 = ['b','c','d','b','c','a','a']   
l2 = []   
for i in l1:   
    if not i in l2:   
        l2.append(i)   
print l2   
上面的代码也可以这样写   
l1 = ['b','c','d','b','c','a','a']   
l2 = []   
[l2.append(i) for i in l1 if not i in l2]   
print l2   
    
    
这样就可以保证排序不变了：   
['b', 'c', 'd', 'a']