operator.itemgetter

https://www.cnblogs.com/dreamer-fish/p/5522687.html

#!/usr/bin/env python3
# -*- coding: utf-8 -*-


from operator import itemgetter  # itemgetter用来去dict中的key，省去了使用lambda函数
from itertools import groupby  # itertool还包含有其他很多函数，比如将多个list联合起来。

d1 = {'name': 'zhangsan', 'age': 20, 'country': 'China'}
d2 = {'name': 'wangwu', 'age': 19, 'country': 'USA'}
d3 = {'name': 'lisi', 'age': 22, 'country': 'JP'}
d4 = {'name': 'zhaoliu', 'age': 22, 'country': 'USA'}
d5 = {'name': 'pengqi', 'age': 22, 'country': 'USA'}
d6 = {'name': 'lijiu', 'age': 22, 'country': 'China'}
lst = [d1, d2, d3, d4, d5, d6]

# 通过country进行分组：
# 需要先排序，然后才能groupby。lst排序后自身被改变
lst.sort(key=itemgetter('country'), reverse=True)  

for i in lst:
    print(i)

lstg = groupby(lst, itemgetter('country'))
# lstg = groupby(lst,key=lambda x:x['country']) 等同于使用itemgetter()

print("-"*30)

for key, group in lstg:
    for g in group:  # group是一个迭代器，包含了所有的分组列表
        print(key, g)

import operator


def cmp_datetime(a, b):
    a_datetime = datetime.datetime.strptime(a, '%Y-%m-%d %H:%M:%S')
    b_datetime = datetime.datetime.strptime(b, '%Y-%m-%d %H:%M:%S')

    if a_datetime > b_datetime:
        return -1
    elif a_datetime < b_datetime:
        return 1
    else:
        return 0


j['data'].sort(cmp=cmp_datetime, key=operator.itemgetter('publish_time'), reverse=-1)

for i in j['data']:
    print str(num) + ",",
    print i['id'] + ",",
    print i['level'] + ",",
    print i['publish_time'] + ","