#全排列
#arr 减一个元素，放入new_arr中
def allpai(arr,new_arr):
    if len(new_arr)==4:
        print(new_arr)
        return
    
    for i in range(len(arr)):
         temp_new=new_arr+[arr[i]]
         temp_arr=arr[:i]+ arr[i+1:]
         allpai(temp_arr,temp_new)
         
new_arr=[]
arr=["a","b","c","d"]
allpai(arr,new_arr)