Converting datetime.date to UTC timestamp in Python

I am dealing with dates in Python and I need to convert them to UTC timestamps to be used inside Javascript. The following code does not work:

>>> d = datetime.date(2011,01,01)
>>> datetime.datetime.utcfromtimestamp(time.mktime(d.timetuple()))
datetime.datetime(2010, 12, 31, 23, 0)

Converting the date object first to datetime also does not help. I tried the example at this link from, but:

from pytz import utc, timezone
from datetime import datetime
from time import mktime
input_date = datetime(year=2011, month=1, day=15)

and now either:

mktime(utc.localize(input_date).utctimetuple())

or

mktime(timezone('US/Eastern').localize(input_date).utctimetuple())

does work.

So general question: how can I get a date converted to seconds since epoch according to UTC?

Solution 1:

If d = date(2011, 1, 1) is in UTC:

>>> from datetime import datetime, date
>>> import calendar
>>> timestamp1 = calendar.timegm(d.timetuple())
>>> datetime.utcfromtimestamp(timestamp1)
datetime.datetime(2011, 1, 1, 0, 0)

If d is in local timezone:

>>> import time
>>> timestamp2 = time.mktime(d.timetuple()) # DO NOT USE IT WITH UTC DATE
>>> datetime.fromtimestamp(timestamp2)
datetime.datetime(2011, 1, 1, 0, 0)

timestamp1 and timestamp2 may differ if midnight in the local timezone is not the same time instance as midnight in UTC.

mktime() may return a wrong result if d corresponds to an ambiguous local time (e.g., during DST transition) or if d is a past(future) date when the utc offset might have been different and the C mktime() has no access to the tz database on the given platform. You could use pytz module (e.g., via tzlocal.get_localzone()) to get access to the tz database on all platforms. Also, utcfromtimestamp() may fail and mktime() may return non-POSIX timestamp if "right" timezone is used.

To convert datetime.date object that represents date in UTC without calendar.timegm():

DAY = 24*60*60 # POSIX day in seconds (exact value)
timestamp = (utc_date.toordinal() - date(1970, 1, 1).toordinal()) * DAY
timestamp = (utc_date - date(1970, 1, 1)).days * DAY

How can I get a date converted to seconds since epoch according to UTC?

To convert datetime.datetime (not datetime.date) object that already represents time in UTC to the corresponding POSIX timestamp (a float).

Python 3.3+

datetime.timestamp():

from datetime import timezone

timestamp = dt.replace(tzinfo=timezone.utc).timestamp()

Note: It is necessary to supply timezone.utc explicitly otherwise .timestamp() assume that your naive datetime object is in local timezone.

Python 3 (< 3.3)

From the docs for datetime.utcfromtimestamp():

There is no method to obtain the timestamp from a datetime instance, but POSIX timestamp corresponding to a datetime instance dt can be easily calculated as follows. For a naive dt:

timestamp = (dt - datetime(1970, 1, 1)) / timedelta(seconds=1)

And for an aware dt:

timestamp = (dt - datetime(1970,1,1, tzinfo=timezone.utc)) / timedelta(seconds=1)

Interesting read: Epoch time vs. time of day on the difference between What time is it? and How many seconds have elapsed?

See also: datetime needs an "epoch" method

Python 2

To adapt the above code for Python 2:

timestamp = (dt - datetime(1970, 1, 1)).total_seconds()

where timedelta.total_seconds() is equivalent to (td.microseconds + (td.seconds + td.days * 24 * 3600) * 10**6) / 10**6 computed with true division enabled.

Example

from __future__ import division
from datetime import datetime, timedelta

def totimestamp(dt, epoch=datetime(1970,1,1)):
    td = dt - epoch
    # return td.total_seconds()
    return (td.microseconds + (td.seconds + td.days * 86400) * 10**6) / 10**6 

now = datetime.utcnow()
print now
print totimestamp(now)

Beware of floating-point issues.

Output

2012-01-08 15:34:10.022403
1326036850.02

How to convert an aware datetime object to POSIX timestamp

assert dt.tzinfo is not None and dt.utcoffset() is not None
timestamp = dt.timestamp() # Python 3.3+

On Python 3:

from datetime import datetime, timedelta, timezone

epoch = datetime(1970, 1, 1, tzinfo=timezone.utc)
timestamp = (dt - epoch) / timedelta(seconds=1)
integer_timestamp = (dt - epoch) // timedelta(seconds=1)

On Python 2:

# utc time = local time              - utc offset
utc_naive  = dt.replace(tzinfo=None) - dt.utcoffset()
timestamp = (utc_naive - datetime(1970, 1, 1)).total_seconds()

Solution 2:

For unix systems only:

>>> import datetime
>>> d = datetime.date(2011, 1, 1)
>>> d.strftime("%s")  # <-- THIS IS THE CODE YOU WANT
'1293832800'

Note 1: dizzyf observed that this applies localized timezones. Don't use in production.

Note 2: Jakub Narębski noted that this ignores timezone information even for offset-aware datetime (tested for Python 2.7).

Solution 3:

• Assumption 1: You're attempting to convert a date to a timestamp, however since a date covers a 24 hour period, there isn't a single timestamp that represents that date. I'll assume that you want to represent the timestamp of that date at midnight (00:00:00.000).

• Assumption 2: The date you present is not associated with a particular time zone, however you want to determine the offset from a particular time zone (UTC). Without knowing the time zone the date is in, it isn't possible to calculate a timestamp for a specific time zone. I'll assume that you want to treat the date as if it is in the local system time zone.

First, you can convert the date instance into a tuple representing the various time components using the timetuple() member:

dtt = d.timetuple() # time.struct_time(tm_year=2011, tm_mon=1, tm_mday=1, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=5, tm_yday=1, tm_isdst=-1)

You can then convert that into a timestamp using time.mktime:

ts = time.mktime(dtt) # 1293868800.0

You can verify this method by testing it with the epoch time itself (1970-01-01), in which case the function should return the timezone offset for the local time zone on that date:

d = datetime.date(1970,1,1)
dtt = d.timetuple() # time.struct_time(tm_year=1970, tm_mon=1, tm_mday=1, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=3, tm_yday=1, tm_isdst=-1)
ts = time.mktime(dtt) # 28800.0

28800.0 is 8 hours, which would be correct for the Pacific time zone (where I'm at).