python从datetime对象减去月份

Question

I would like to substract months and get a result in the form yyyymmdd. To start I am given a string timestamp in sec, then here is what I'm doing:

>>> ts=1454284800
>>> billdate = datetime.datetime.strptime(time.strftime('%Y%m%d', time.gmtime(ts)), '%Y%m%d') - datetime.timedelta(5*365/12.0)
>>> billdate
datetime.datetime(2015, 9, 1, 22, 0)
>>>

In my snippet I substract 5 months, and get datetime.datetime(2015, 9, 1, 22, 0). I would like to get rid of the the hour 22 and get datetime.datetime(2015, 9, 1, 0, 0).

Thanks in advance.

Answer 1

Point 1: 22 is not day. It is hours.

Point 2: If you want to get rid of hours and get datetime for 12:00 AM, then try this:

>>> billdate = datetime.datetime(billdate.year, billdate.month, billdate.day)
>>> billdate
datetime.datetime(2015, 9, 1, 0, 0)

Answer 2

If you want to modify fields of the datetime.datetime object, you need to use replace

billdate = billdate.replace(hour=0)

Quote from the datetime wiki page

datetime.replace([year[, month[, day[, hour[, minute[, second[, microsecond[, tzinfo]]]]]]]])

Return a datetime with the same attributes, except for those attributes given new values by whichever keyword arguments are specified