Python3 list 自定義比較函數

如題，解決Python3中list自定義比較的問題。

1. 定義比較函數

def cmp(a, b):

2. 將其轉換爲鍵函數。下面的包裝解決了這一問題:

def cmp_to_key(mycmp):
    class K:
        def __init__(self, obj, *args):
            self.obj = obj
        def __lt__(self, other):
            return mycmp(self.obj, other.obj) < 0
        def __gt__(self, other):
            return mycmp(self.obj, other.obj) > 0
        def __eq__(self, other):
            return mycmp(self.obj, other.obj) == 0
        def __le__(self, other):
            return mycmp(self.obj, other.obj) <= 0
        def __ge__(self, other):
            return mycmp(self.obj, other.obj) >= 0
        def __ne__(self, other):
            return mycmp(self.obj, other.obj) != 0
    return K

3. 調用比進行比較

li_sort = sorted(li, key=cmp_to_key(cmp), reverse=True)