python groupby函数

rows = [
 {'address': '5412 N CLARK', 'date': '07/01/2012'},
 {'address': '5148 N CLARK', 'date': '07/04/2012'},
 {'address': '5800 E 58TH', 'date': '07/02/2012'},
 {'address': '2122 N CLARK', 'date': '07/03/2012'},
 {'address': '5645 N RAVENSWOOD', 'date': '07/02/2012'},
 {'address': '1060 W ADDISON', 'date': '07/02/2012'},
 {'address': '4801 N BROADWAY', 'date': '07/01/2012'},
 {'address': '1039 W GRANVILLE', 'date': '07/04/2012'},
 ]
from operator import itemgetter
 from itertools import groupby

rows.sort(key=itemgetter('date'))

for date, items in groupby(rows, key=itemgetter('date')):
 print(date)
 for i in items:
 print(' ', i)

07/01/2012
 {'date': '07/01/2012', 'address': '5412 N CLARK'}
 {'date': '07/01/2012', 'address': '4801 N BROADWAY'}
 07/02/2012
 {'date': '07/02/2012', 'address': '5800 E 58TH'}
 {'date': '07/02/2012', 'address': '5645 N RAVENSWOOD'}
 {'date': '07/02/2012', 'address': '1060 W ADDISON'}
 07/03/2012
 {'date': '07/03/2012', 'address': '2122 N CLARK'}
 07/04/2012
 {'date': '07/04/2012', 'address': '5148 N CLARK'}
 {'date': '07/04/2012', 'address': '1039 W GRANVILLE'}