>>> dt = datetime.datetime.now()
>>> dt = dt.replace(hour=0, minute=0, second=0, microsecond=0) # Returns a copy
>>> dt
datetime.datetime(2011, 3, 29, 0, 0)

>>> d_truncated = datetime.date(dt.year, dt.month, dt.day)
>>> d_truncated
datetime.date(2011, 3, 29)

>>> now = datetime.now()
>>> now.date()
datetime.date(2011, 3, 29)

>>> now.replace(minute=0, hour=0, second=0, microsecond=0)
datetime.datetime(2011, 3, 29, 0, 0)

dt = datetime.date.today()
dt = datetime.datetime(dt.year, dt.month, dt.day)

newdatetime = now.replace(hour=0, minute=0, second=0, microsecond=0)

>>> from datetime import datetime, time
>>> dt = datetime.utcnow()
>>> dt.date()
datetime.date(2015, 2, 3)
>>> datetime.combine(dt, time.min)
datetime.datetime(2015, 2, 3, 0, 0)

from datetime import datetime
d = datetime.today()

# Retrieves the day and the year
print d.strftime("%d-%Y")

29-2011

from datetime import datetime
d = datetime.today()

# Retrieves the day
print d.day

29

import datetime
from delorean import Delorean
now = datetime.datetime.now()
d = Delorean(now, timezone='US/Pacific)

>>> now
datetime.datetime(2015, 3, 26, 19, 46, 40, 525703)

>>> d.truncate('second')
Delorean(datetime=2015-03-26 19:46:40-07:00, timezone=US/Pacific)

>>> d.truncate('minute')
Delorean(datetime=2015-03-26 19:46:00-07:00, timezone=US/Pacific)

>>> d.truncate('hour')
Delorean(datetime=2015-03-26 19:00:00-07:00, timezone=US/Pacific)

>>> d.truncate('day')
Delorean(datetime=2015-03-26 00:00:00-07:00, timezone=US/Pacific)

>>> d.truncate('month')
Delorean(datetime=2015-03-01 00:00:00-07:00, timezone=US/Pacific)

>>> d.truncate('year')
Delorean(datetime=2015-01-01 00:00:00-07:00, timezone=US/Pacific)

>>> d.truncate('year').datetime
datetime.datetime(2015, 1, 1, 0, 0, tzinfo=<DstTzInfo 'US/Pacific' PDT-1 day, 17:00:00 DST>)

import numpy as np
dates_array = np.array(['2013-01-01', '2013-01-15', '2013-01-30']).astype('datetime64[ns]')
truncated_dates = dates_array.astype('datetime64[D]')