看了西红柿的博客，此文纯搬运，方便自己查询用。
原文：https://www.cnblogs.com/tomato0906/articles/4890701.html
1、python中的字符串类型是不允许直接修改元素的。必须先把要排序的字符串放在容器里，如list。
python中list容器的sort（）函数没有返回值。所以在python中对字符串排序需要好几行代码：
s=”string”
l=list(s)
l.sort()
s=””.join(l)
print s ‘ginrst’
一行代码搞定字符串排序的方法：
s=”string”
s=””.join((lambda x:(x.sort(),x)[1])(list(s)))
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string = ””’
the stirng
Has many
line In
THE fIle”’list_of_string=string.split()print list_of_string #将字符串分离开，放入列表中
print ‘*’*50
defcase_insensitive_sort(liststring):
listtemp= [(x.lower(),x) for x in liststring] #将字符串列表，生成元组，（忽略大小写的字符串，字符串）
listtemp.sort() #对元组排序，因为元组为：（忽略大小写的字符串，字符串），就是按忽略大小写的字符串排序
return [x[1] for x in listtemp] #排序完成后，返回原字符串的列表
print case_insensitive_sort(list_of_string) #调用起来，测试一下
2、使用内建函数
sorted(iterable[,cmp[, key[,reverse]]])
Return a new sorted list from the items in iterable.
key specifies a function of one argument that is used to extract a comparison key from each list element:key=str.lower. The default value isNone.
使用参数key=str.lower
代码如下：
defcase_insensitive_sort2(liststring):return sorted(liststring,key = str.lower)
3、
使用list的sort方法：
The sort() method takes optional arguments for controlling the comparisons.
cmp specifies a custom comparison function of two arguments (list items) 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()). The default value is None.
key specifies a function of one argument that is used to extract a comparison key from each list element: key=str.lower. The default value is None.
reverse is a boolean value. If set to True, then the list elements are sorted as if each comparison were reversed
defcase_insensitive_sort3(liststring):
liststring.sort(cmp=lambdax,y: cmp(x.lower(), y.lower()))
case_insensitive_sort3(list_of_string)print list_of_string
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根据字符串长度来排序
给定字符串：xs = [‘dddd’,’a’,’bb’,’ccc’]
输出排序的结果：[‘a’,’bb’,’ccc’,’dddd’]
解决1：
xs.sort(key=len)
解决2：
xs.sort(lambda x,y: cmp(len(x), len(y))
注意：当传递lambda给sort时，需要返回integer，而不能为bool数
使用：
xs.sort(lambda x,y: len(x) < len(y))则不对。
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python根据字符串中的内嵌的数字排序
l = [ ‘ch9.txt’, ‘ch10.txt’, ‘ch1.txt’, ‘ch3.txt’, ‘ch11.txt’ ]
排序完成后
l=[ ‘ch1.txt’, ‘ch3.txt’, ‘ch9.txt’, ‘ch10.txt’, ‘ch11.txt’ ]
import re
l = [ ‘ch9.txt’, ‘ch10.txt’, ‘ch1.txt’, ‘ch3.txt’, ‘ch11.txt’ ]
p = re.compile(“(\d+)”)
def my_cmp(v1, v2):
d1 = [int(i) for i in p.findall(v1)][0]
d2 = [int(i) for i in p.findall(v2)][0]
return cmp(d1, d2)
l.sort(my_cmp)
print l
>>> import re
>>>
>>> l = [ ‘ch9.txt’, ‘ch10.txt’, ‘ch1.txt’, ‘ch3.txt’, ‘ch11.txt’ ]
>>>
>>> p = re.compile(“(\d+)”)
>>>
>>> def my_cmp(v1, v2):
… d1 = [int(i) for i in p.findall(v1)][0]
… d2 = [int(i) for i in p.findall(v2)][0]
… return cmp(d1, d2)
…
>>>
… l.sort(my_cmp)
>>>
>>> print l
[‘ch1.txt’, ‘ch3.txt’, ‘ch9.txt’, ‘ch10.txt’, ‘ch11.txt’]
>>>
一句代码足以
l.sort(key = lambda x:int(re.match(‘\D+(\d+)\.txt’,x).group(1)))