很多時候，我們需要對List進(jìn)行排序，Python提供了兩個方法，對給定的List L進(jìn)行排序：
方法1.用List的成員函數(shù)sort進(jìn)行排序
方法2.用built-in函數(shù)sorted進(jìn)行排序（從2.4開始）
這兩種方法使用起來差不多，以第一種為例進(jìn)行講解：
從Python2.4開始，sort方法有了三個可選的參數(shù)，Python Library Reference里是這樣描述的
代碼如下:
cmp:cmp specifies a custom comparison function of two arguments (iterable elements) which should return a negative, zero or positive number depending on whether the first argument is considered smaller than, equal to, or larger than the second argument:
"cmp=lambda x,y: cmp(x.lower(), y.lower())"
key:key specifies a function of one argument that is used to extract a comparison key from each list element: "key=str.lower"
reverse:reverse is a boolean value. If set to True, then the list elements are sorted as if each comparison were reversed.In general, the key and reverse conversion processes are much faster than specifying an
equivalent cmp function. This is because cmp is called multiple times for each list element while key and reverse touch each element only once.
以下是sort的具體實例。
實例1:
代碼如下:
>>>L = [2,3,1,4]
>>>L.sort()
>>>L
>>>[1,2,3,4]
實例2:
代碼如下:
>>>L = [2,3,1,4]
>>>L.sort(reverse=True)
>>>L
>>>[4,3,2,1]
實例3:
代碼如下:
>>>L = [('b',2),('a',1),('c',3),('d',4)]
>>>L.sort(cmp=lambda x,y:cmp(x[1],y[1]))
>>>L
>>>[('a', 1), ('b', 2), ('c', 3), ('d', 4)]
實例4:
代碼如下:
>>>L = [('b',2),('a',1),('c',3),('d',4)]
>>>L.sort(key=lambda x:x[1])
>>>L
>>>[('a', 1), ('b', 2), ('c', 3), ('d', 4)]
實例5:
代碼如下:
>>>L = [('b',2),('a',1),('c',3),('d',4)]
>>>import operator
>>>L.sort(key=operator.itemgetter(1))
>>>L
>>>[('a', 1), ('b', 2), ('c', 3), ('d', 4)]
實例6:(DSU方法:Decorate-Sort-Undercorate)
代碼如下:
>>>L = [('b',2),('a',1),('c',3),('d',4)]
>>>A = [(x[1],i,x) for i,x in enumerate(L)] #i can confirm the stable sort
>>>A.sort()
>>>L = [s[2] for s in A]
>>>L
>>>[('a', 1), ('b', 2), ('c', 3), ('d', 4)]
以上給出了6中對List排序的方法，其中實例3.4.5.6能起到對以List item中的某一項
為比較關(guān)鍵字進(jìn)行排序.
效率比較：
代碼如下:
cmp < DSU < key
通過實驗比較，方法3比方法6要慢，方法6比方法4要慢，方法4和方法5基本相當(dāng)
多關(guān)鍵字比較排序：
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