6 itemgetter和key函数

注意到sort和groupby所用的key函数，除了lambda写法外，还有一种简写，就是使用itemgetter：

a = [{'date': '2019-12-15', 'weather': 'cloud'},
 {'date': '2019-12-13', 'weather': 'sunny'},
 {'date': '2019-12-14', 'weather': 'cloud'}]
from operator import itemgetter
from itertools import groupby

a.sort(key=itemgetter('weather'))
for k, items in groupby(a, key=itemgetter('weather')):
     print(k)
     for i in items:
         print(i)

结果：

cloud
{'date': '2019-12-15', 'weather': 'cloud'}
{'date': '2019-12-14', 'weather': 'cloud'}
sunny
{'date': '2019-12-13', 'weather': 'sunny'}