Python min函数,带有一个对象列表

Question

如何使用函数的key参数min来比较对象的1个属性列表？

例

class SpecialNumber:
    def __init__(self, i):
        self.number = i

li = [SpecialNumber(1), SpecialNumber(3), SpecialNumber(2)]

Answer 1

http://docs.python.org/library/operator.html#operator.attrgetter

from operator import attrgetter
min_num = min(li,key=attrgetter('number'))

交互式会话示例:

>>> li = [SpecialNumber(1), SpecialNumber(3), SpecialNumber(2)]
>>> [i.number for i in li]
[1, 3, 2]
>>> min_num = min(li,key=attrgetter('number'))
>>> print min_num.number
1

Answer 2

它的:

min(li, key=lambda x: x.number)

你需要一个接受a SpecialNumber并返回其元素的函数.

Answer 3

我是通过压倒来做到的 __cmp__

class SpecialNumber:
    def __init__(self, i):
        self.number = i

    def __repr__(self):
        return '<SpecialNumber(%d)>' % self.number

    def __cmp__(self, other):
        return cmp(self.number, other.number)

li = [SpecialNumber(1), SpecialNumber(3), SpecialNumber(2)]
print min(li) # <SpecialNumber(1)>