如何在python sorted(list)中指定2个键? [英] How to specify 2 keys in python sorted(list)?

问题描述

如何首先按key=len然后按key=str对字符串列表进行排序? 我已经尝试了以下方法，但是没有给我想要的排序方式:

How do I sort a list of strings by key=len first then by key=str? I've tried the following but it's not giving me the desired sort:

>>> ls = ['foo','bar','foobar','barbar']
>>> 
>>> for i in sorted(ls):
...     print i
... 
bar
barbar
foo
foobar
>>>
>>> for i in sorted(ls, key=len):
...     print i
... 
foo
bar
foobar
barbar
>>> 
>>> for i in sorted(ls, key=str):
...     print i
... 
bar
barbar
foo
foobar

我需要得到:

bar
foo
barbar
foobar

推荐答案

定义一个返回一个元组的键函数，其中第一项为len(str)，第二项为字符串本身.然后在字典上比较元组.也就是说，首先将长度进行比较；然后再对长度进行比较.如果它们相等，则将字符串进行比较.

Define a key function that returns a tuple in which the first item is len(str) and the second one is the string itself. Tuples are then compared lexicographically. That is, first the lengths are compared; if they are equal then the strings get compared.

In [1]: ls = ['foo','bar','foobar','barbar']

In [2]: sorted(ls, key=lambda s: (len(s), s))
Out[2]: ['bar', 'foo', 'barbar', 'foobar']

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