How to convert Python UTC datetime object to UNIX timestamp

by Ruslan Spivak on July 20, 2011

I seem to get this question every half a year and every time I have difficulties remembering how to do it.

>>> from datetime import datetime
>>> d = datetime.utcnow()
>>> d
datetime.datetime(2011, 7, 21, 3, 13, 22, 259901)

So here is the snippet that I use to convert datetime to timestamp:

>>> import calendar
>>> calendar.timegm(d.utctimetuple())
1311218002

Let’s verify it:

$ date -ud @1311218002
Thu Jul 21 03:13:22 UTC 2011

Looks fine, but I can’t for the life of me understand why the function timegm is part of the calendar module.

From Python official documentation:

calendar.timegm(tuple): An unrelated but handy function that takes a time tuple such as returned by the gmtime() function in the time module, and returns the corresponding Unix timestamp value, assuming an epoch of 1970, and the POSIX encoding. In fact, time.gmtime() and timegm() are each others’ inverse.

{ 8 comments… read them below or add one }

datetime objects can do that as well using `strftime`:

In [7]: d = datetime.datetime(2011, 7, 21, 3, 13, 22, 259901)

In [8]: d.strftime(‘%s’)
Out[8]: ’1311210802′

Ruslan Spivak July 21, 2011 at 8:00 PM: Unfortunately timezone-aware datetime objects (UTC) incorrectly calculate UNIX timestamp:
[sourcecode language="python"]
>>> import pytz
>>> import datetime
>>> utc = pytz.timezone(‘UTC’)
>>> toronto = pytz.timezone(‘America/Toronto’)
>>> a = datetime.datetime(2011, 7, 21, 3, 13, 22, tzinfo=utc)
>>> b = a.astimezone(toronto)
>>> a.strftime(‘%s’)
’1311236002′
>>> b.strftime(‘%s’)
’1311218002′
[/sourcecode]

Reply

>>> import datetime
>>> import time
>>> d = datetime.datetime(2011, 7, 21, 3, 13, 22, 259901)
>>> time.mktime(d.timetuple())
1311210802.0

Probably the more basic way.

Ruslan Spivak July 21, 2011 at 8:09 PM: time.mktime(t) returns timestamp in local time:
[sourcecode language="python"]
>>> import pytz
>>> import datetime
>>> import time
>>>
>>> utc = pytz.timezone(‘UTC’)
>>> d = datetime.datetime(2011, 7, 21, 3, 13, 22, tzinfo=utc)
>>> time.mktime(d.timetuple())
1311236002.0
[/sourcecode]

Reply

So why so much way to do it ?
why not “totimestamp” in datetime like the “fromtimestamp” method?

Ruslan Spivak July 22, 2011 at 5:42 AM: Well, technically there are not many correct ways to do it. But I agree with the API question, having that call would make conversion process clear and unambiguous.

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