Python如何根据日期创建子列表？

Question

我有一个这样的列表:

my = [datetime.datetime(2013, 11, 12, 20, 22, 5),
     datetime.datetime(2013, 11, 12, 20, 21, 27),
     datetime.datetime(2013, 11, 12, 20, 20, 28),
     datetime.datetime(2013, 11, 11, 18, 21, 27),
     datetime.datetime(2013, 11, 11, 15, 21, 27),
     datetime.datetime(2013, 11, 11, 11, 21, 27),
     datetime.datetime(2013, 11, 10, 9, 21, 27),
     datetime.datetime(2013, 11, 10, 19, 21, 27),
     datetime.datetime(2013, 11, 10, 22, 21, 27),
     datetime.datetime(2013, 11, 10, 20, 21, 27)]

我想按天创建列表到另一个列表中，我使用 [n].date() 来比较日期并加入它们，但我在绕圈子却没有得到它，请有人帮助我吗？

预期结果:

    days = [
    [datetime.datetime(2013, 11, 12, 20, 22, 5), datetime.datetime(2013, 11, 12, 20, 21, 27), datetime.datetime(2013, 11, 12, 20, 20, 28)],
    [datetime.datetime(2013, 11, 11, 18, 21, 27),datetime.datetime(2013, 11, 11, 15, 21, 27),datetime.datetime(2013, 11, 11, 11, 21, 27)],
    [datetime.datetime(2013, 11, 10, 9, 21, 27),datetime.datetime(2013, 11, 10, 19, 21, 27),datetime.datetime(2013, 11, 10, 22, 21, 27),datetime.datetime(2013, 11, 10, 20, 21, 27)]
           ]

尝试失败:

In [152]: fecha = None
   .....: dia = []
   .....: days = []
   .....: for i in my:
   .....:     if fecha:
   .....:         if i.date() == fecha:
   .....:             dia.append(i)
   .....:         else:
   .....:             days.append(dia)
   .....:             fecha = i.date()
   .....:     else:
   .....:         fecha = i.date()

谢谢

Answer 1

使用itertools.groupby并使用key = datetime.date()进行分组:

.date() 在 datetime 对象上返回 date 对象，我们可以使用它来对列表中的项目进行分组:

>>> my[0].date()
datetime.date(2013, 11, 12)

演示:

>>> from pprint import pprint
>>> from itertools import groupby
>>> pprint([list(g) for k, g in groupby(my, key=lambda x:x.date())])
[[datetime.datetime(2013, 11, 12, 20, 22, 5),
  datetime.datetime(2013, 11, 12, 20, 21, 27),
  datetime.datetime(2013, 11, 12, 20, 20, 28)],
 [datetime.datetime(2013, 11, 11, 18, 21, 27),
  datetime.datetime(2013, 11, 11, 15, 21, 27),
  datetime.datetime(2013, 11, 11, 11, 21, 27)],
 [datetime.datetime(2013, 11, 10, 9, 21, 27),
  datetime.datetime(2013, 11, 10, 19, 21, 27),
  datetime.datetime(2013, 11, 10, 22, 21, 27),
  datetime.datetime(2013, 11, 10, 20, 21, 27)]]

如果键尚未按日期排序，则使用 collections.defaultdict(list) 并使用 datetime.date() 作为键。