按属性[重复]对对象列表进行排序

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I am trying to sort a list of objects in python, however this code will not work:

我试图在python中对对象列表进行排序,但是这段代码不起作用:

import datetime

class Day:
    def __init__(self, date, text):
        self.date = date
        self.text = text

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

mylist = [Day(datetime.date(2009, 01, 02), "Jan 2"), Day(datetime.date(2009, 01, 01), "Jan 1")]
print mylist
print mylist.sort()

The output of this is:

这个输出是:

[<__main__.Day instance at 0x519e0>, <__main__.Day instance at 0x51a08>]
None

Could somebody show me a good way solve this? Why is the sort() function returning None?

有人能告诉我解决这个问题的好方法吗?为什么sort()函数返回None?

2 个解决方案

#1

mylist.sort() returns nothing, it sorts the list in place. Change it to

mylist.sort()不返回任何内容,它会对列表进行排序。将其更改为

mylist.sort()
print mylist

to see the correct result.

看到正确的结果。

See http://docs.python.org/library/stdtypes.html#mutable-sequence-types note 7.

请参阅http://docs.python.org/library/stdtypes.html#mutable-sequence-types注7。

The sort() and reverse() methods modify the list in place for economy of space when sorting or reversing a large list. To remind you that they operate by side effect, they don’t return the sorted or reversed list.

sort()和reverse()方法在排序或反转大型列表时修改列表以便节省空间。为了提醒您它们是由副作用操作的,它们不会返回已排序或反转的列表。

#2

See sorted for a function that will return a sorted copy of any iterable.

请参阅排序函数,该函数将返回任何iterable的排序副本。

#1