Python UTC datetime object's ISO format doesn't include Z (Zulu or Zero offset)


Why python 2.7 doesn’t include Z character (Zulu or zero offset) at the end of UTC datetime object’s isoformat string unlike JavaScript?

>>> datetime.datetime.utcnow().isoformat()

Whereas in javascript

>>>  console.log(new Date().toISOString()); 
Asked By: Murali Mopuru



Python datetime objects don’t have time zone info by default, and without it, Python actually violates the ISO 8601 specification (if no time zone info is given, assumed to be local time). You can use the pytz package to get some default time zones, or directly subclass tzinfo yourself:

from datetime import datetime, tzinfo, timedelta
class simple_utc(tzinfo):
    def tzname(self,**kwargs):
        return "UTC"
    def utcoffset(self, dt):
        return timedelta(0)

Then you can manually add the time zone info to utcnow():

>>> datetime.utcnow().replace(tzinfo=simple_utc()).isoformat()

Note that this DOES conform to the ISO 8601 format, which allows for either Z or +00:00 as the suffix for UTC. Note that the latter actually conforms to the standard better, with how time zones are represented in general (UTC is a special case.)

Answered By: stiv

Python datetimes are a little clunky. Use arrow.

> str(arrow.utcnow())

Arrow has essentially the same api as datetime, but with timezones and some extra niceties that should be in the main library.

A format compatible with Javascript can be achieved by:

arrow.utcnow().isoformat().replace("+00:00", "Z")

Javascript Date.parse will quietly drop microseconds from the timestamp.

Answered By: U2EF1

Option: isoformat()

Python’s datetime does not support the military timezone suffixes like ‘Z’ suffix for UTC. The following simple string replacement does the trick:

In [1]: import datetime

In [2]: d = datetime.datetime(2014, 12, 10, 12, 0, 0)

In [3]: str(d).replace('+00:00', 'Z')
Out[3]: '2014-12-10 12:00:00Z'

str(d) is essentially the same as d.isoformat(sep=' ')

See: Datetime, Python Standard Library

Option: strftime()

Or you could use strftime to achieve the same effect:

In [4]: d.strftime('%Y-%m-%dT%H:%M:%SZ')
Out[4]: '2014-12-10T12:00:00Z'

Note: This option works only when you know the date specified is in UTC.

See: datetime.strftime()

Additional: Human Readable Timezone

Going further, you may be interested in displaying human readable timezone information, pytz with strftime %Z timezone flag:

In [5]: import pytz

In [6]: d = datetime.datetime(2014, 12, 10, 12, 0, 0, tzinfo=pytz.utc)

In [7]: d
Out[7]: datetime.datetime(2014, 12, 10, 12, 0, tzinfo=<UTC>)

In [8]: d.strftime('%Y-%m-%d %H:%M:%S %Z')
Out[8]: '2014-12-10 12:00:00 UTC'
Answered By: Manav Kataria

By combining all answers above I came with following function :

from datetime import datetime, tzinfo, timedelta
class simple_utc(tzinfo):
    def tzname(self,**kwargs):
        return "UTC"
    def utcoffset(self, dt):
        return timedelta(0)

def getdata(yy, mm, dd, h, m, s) :
    d = datetime(yy, mm, dd, h, m, s)
    d = d.replace(tzinfo=simple_utc()).isoformat()
    d = str(d).replace('+00:00', 'Z')
    return d

print getdata(2018, 02, 03, 15, 0, 14)
Answered By: EmptyData

There are a lot of good answers on the post, but I wanted the format to come out exactly as it does with JavaScript. This is what I’m using and it works well.

In [1]: import datetime

In [1]: now = datetime.datetime.utcnow()

In [1]: now.strftime('%Y-%m-%dT%H:%M:%S') + now.strftime('.%f')[:4] + 'Z'
Out[3]: '2018-10-16T13:18:34.856Z'
Answered By: Michael Cox
>>> import arrow

>>> now = arrow.utcnow().format('YYYY-MM-DDTHH:mm:ss.SSS')
>>> now
>>> zulu = "{}Z".format(now)
>>> zulu

Or, to get it in one fell swoop:

>>> arrow.utcnow().format("YYYY-MM-DDTHH:mm:ss.SSS[Z]")
Answered By: digitalshadow

The following javascript and python scripts give identical outputs. I think it’s what you are looking for.


new Date().toISOString()


from datetime import datetime


The output they give is the UTC (zulu) time formatted as an ISO string with a 3 millisecond significant digit and appended with a Z.

Answered By: Clay Risser

In Python >= 3.2 you can simply use this:

>>> from datetime import datetime, timezone
Answered By: Michel Samia
pip install python-dateutil
>>> a = "2019-06-27T02:14:49.443814497Z"
>>> dateutil.parser.parse(a)
datetime.datetime(2019, 6, 27, 2, 14, 49, 443814, tzinfo=tzutc())
Answered By: W Yg

I use pendulum:

import pendulum

d ="UTC").to_iso8601_string()

>>> 2019-10-30T00:11:21.818265Z
Answered By: Jason Baker

Your goal shouldn’t be to add a Z character, it should be to generate a UTC "aware" datetime string in ISO 8601 format. The solution is to pass a UTC timezone object to instead of using datetime.utcnow():

from datetime import datetime, timezone
>>> datetime.datetime(2020, 1, 8, 6, 6, 24, 260810, tzinfo=datetime.timezone.utc)
>>> '2020-01-08T06:07:04.492045+00:00'

That looks good, so let’s see what Django and dateutil think:

from django.utils.timezone import is_aware
>>> True

from dateutil.parser import isoparse
>>> True

Note that you need to use isoparse() from dateutil.parser because the Python documentation for datetime.fromisoformat() says it "does not support parsing arbitrary ISO 8601 strings".

Okay, the Python datetime object and the ISO 8601 string are both UTC "aware". Now let’s look at what JavaScript thinks of the datetime string. Borrowing from this answer we get:

let date = '2020-01-08T06:07:04.492045+00:00';
const dateParsed = new Date(Date.parse(date))

// Tue Jan 07 2020 22:07:04 GMT-0800 (Pacific Standard Time)

// 2020-01-08T06:07:04.492Z

// Wed, 08 Jan 2020 06:07:04 GMT


I approached this problem with a few goals:

  • generate a UTC "aware" datetime string in ISO 8601 format
  • use only Python Standard Library functions for datetime object and string creation
  • validate the datetime object and string with the Django timezone utility function, the dateutil parser and JavaScript functions

Note that this approach does not include a Z suffix and does not use utcnow(). But it’s based on the recommendation in the Python documentation and it passes muster with both Django and JavaScript.

See also:

Answered By: highpost

Short answer"+00:00", "Z")

Long answer

The reason that the "Z" is not included is because and even datetime.utcnow() return timezone naive datetimes, that is to say datetimes with no timezone information associated. To get a timezone aware datetime, you need to pass a timezone as an argument to For example:

from datetime import datetime, timezone

#> datetime.datetime(2020, 9, 3, 20, 58, 49, 22253)
# This is timezone naive
#> datetime.datetime(2020, 9, 3, 20, 58, 49, 22253, tzinfo=datetime.timezone.utc)
# This is timezone aware

Once you have a timezone aware timestamp, isoformat will include a timezone designation. Thus, you can then get an ISO 8601 timestamp via:
#> '2020-09-03T20:53:07.337670+00:00'

"+00:00" is a valid ISO 8601 timezone designation for UTC. If you want to have "Z" instead of "+00:00", you have to do the replacement yourself:"+00:00", "Z")
#> '2020-09-03T20:53:07.337670Z'
Answered By: Zags

Using only standard libraries, making no assumption that the timezone is already UTC, and returning the exact format requested in the question:

dt.astimezone(timezone.utc).replace(tzinfo=None).isoformat(timespec='milliseconds') + 'Z'

This does require Python 3.6 or later though.

Answered By: Ian Goldby