#2.去除列表中的重复元素

 #set方法

def removeDuplicates_set(nums):

    l2 = list(set(l1))

    #用l1的顺序排序l2

    #l2.sort(key=l1.index)

    return l2

 #重构字典方法

def removeDuplicates_dict_fromkeys(nums):

    l2 = {}.fromkeys(nums).keys()

    return list(l2)

 #列表推到式，普通方法

def removeDuplicates_normal(nums):

    l2 = []

    [l2.append(i) for i in nums if not i in l2]

    return list(l2)

if __name__=='__main__':

    l1 = ['b','c','d','b','c','a','a']

    print (removeDuplicates_normal(l1))