如何在 Python 中比较日期和日期时间？
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How can I compare a date and a datetime in Python?
提问by Mridang Agarwalla
Here's a little snippet that I'm trying execute:
这是我正在尝试执行的一个小片段：
>>> from datetime import *
>>> item_date = datetime.strptime('7/16/10', "%m/%d/%y")
>>> from_date = date.today()-timedelta(days=3)
>>> print type(item_date)
<type 'datetime.datetime'>
>>> print type(from_date)
<type 'datetime.date'>
>>> if item_date > from_date:
... print 'item is newer'
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: can't compare datetime.datetime to datetime.date
I can't seem to compare the date and the datetime values. What would be the best way to compare these? Should I convert the datetime to date or vice-versa? How do i convert between them.
我似乎无法比较日期和日期时间值。比较这些的最佳方法是什么？我应该将日期时间转换为日期，反之亦然？我如何在它们之间转换。
(A small question but it seems to be a little confusing.)
（一个小问题，但似乎有点令人困惑。）
采纳答案by kennytm
Use the .date()methodto convert a datetime to a date:
使用该.date()方法将日期时间转换为日期：
if item_date.date() > from_date:
Alternatively, you could use datetime.today()instead of date.today(). You could use
或者，您可以使用datetime.today()代替date.today(). 你可以用
from_date = from_date.replace(hour=0, minute=0, second=0, microsecond=0)
to eliminate the time part afterwards.
以消除之后的时间部分。
回答by samarth
I am trying to compare date which are in string format like '20110930'
我正在尝试比较字符串格式的日期，例如“20110930”
benchMark = datetime.datetime.strptime('20110701', "%Y%m%d")
actualDate = datetime.datetime.strptime('20110930', "%Y%m%d")
if actualDate.date() < benchMark.date():
print True
回答by tobixen
In my case, I get two objects in and I don't know if it's date or timedate objects. Converting to date won't be good as I'd be dropping information - two timedate objects with the same date should be sorted correctly. I'm OK with the dates being sorted before the datetime with same date.
在我的例子中，我得到了两个对象，我不知道它是 date 还是 timedate 对象。转换为日期不会好，因为我会丢弃信息 - 应该正确排序两个具有相同日期的 timedate 对象。我可以将日期排序在具有相同日期的日期时间之前。
I think I will use strftime before comparing:
我想我会在比较之前使用 strftime ：
>>> foo=datetime.date(2015,1,10)
>>> bar=datetime.datetime(2015,2,11,15,00)
>>> foo.strftime('%F%H%M%S') > bar.strftime('%F%H%M%S')
False
>>> foo.strftime('%F%H%M%S') < bar.strftime('%F%H%M%S')
True
Not elegant, but should work out. I think it would be better if Python wouldn't raise the error, I see no reasons why a datetime shouldn't be comparable with a date. This behaviour is consistent in python2 and python3.
不优雅，但应该工作。我认为如果 Python 不引发错误会更好，我认为没有理由不能将日期时间与日期进行比较。这种行为在 python2 和 python3 中是一致的。
回答by tobixen
Here is another take, "stolen" from a comment at can't compare datetime.datetime to datetime.date... convert the date to a datetime using this construct:
这是另一种观点，“被盗”从评论中无法比较 datetime.datetime 到 datetime.date...使用此构造将日期转换为日期时间：
datetime.datetime(d.year, d.month, d.day)
Suggestion:
建议：
from datetime import datetime
def ensure_datetime(d):
"""
Takes a date or a datetime as input, outputs a datetime
"""
if isinstance(d, datetime):
return d
return datetime.datetime(d.year, d.month, d.day)
def datetime_cmp(d1, d2):
"""
Compares two timestamps. Tolerates dates.
"""
return cmp(ensure_datetime(d1), ensure_datetime(d2))
回答by Peko Chan
Create and similar object for comparison works too ex:
用于比较的创建和类似对象也适用，例如：
from datetime import datetime, date
now = datetime.now()
today = date.today()
# compare now with today
two_month_earlier = date(now.year, now.month - 2, now.day)
if two_month_earlier > today:
print(True)
two_month_earlier = datetime(now.year, now.month - 2, now.day)
if two_month_earlier > now:
print("this will work with datetime too")
