isoparse function from python-dateutil

The python-dateutil package has dateutil.parser.isoparse to parse not only RFC 3339 datetime strings like the one in the question, but also other ISO 8601 date and time strings that don't comply with RFC 3339 (such as ones with no UTC offset, or ones that represent only a date).

>>> import dateutil.parser
>>> dateutil.parser.isoparse('2008-09-03T20:56:35.450686Z') # RFC 3339 format
datetime.datetime(2008, 9, 3, 20, 56, 35, 450686, tzinfo=tzutc())
>>> dateutil.parser.isoparse('2008-09-03T20:56:35.450686') # ISO 8601 extended format
datetime.datetime(2008, 9, 3, 20, 56, 35, 450686)
>>> dateutil.parser.isoparse('20080903T205635.450686') # ISO 8601 basic format
datetime.datetime(2008, 9, 3, 20, 56, 35, 450686)
>>> dateutil.parser.isoparse('20080903') # ISO 8601 basic format, date only
datetime.datetime(2008, 9, 3, 0, 0)

The python-dateutil package also has dateutil.parser.parse. Compared with isoparse, it is presumably less strict, but both of them are quite forgiving and will attempt to interpret the string that you pass in. If you want to eliminate the possibility of any misreads, you need to use something stricter than either of these functions.

Comparison with Python 3.7+’s built-in datetime.datetime.fromisoformat

dateutil.parser.isoparse is a full ISO-8601 format parser, but in Python ≤ 3.10 fromisoformat is deliberately not. In Python 3.11, fromisoformat supports almost all strings in valid ISO 8601. See fromisoformat's docs for this cautionary caveat. (See this answer).

Since Python 3.11, the standard library’s datetime.datetime.fromisoformat supports most valid ISO 8601 input (and some non-valid input, see docs). In earlier versions it only parses a specific subset, see the cautionary note at the end of the docs. If you are using Python 3.10 or earlier on strings that don't fall into that subset (like in the question), see other answers for functions from outside the standard library.

The current docs (so exceptions listed are still valid for Python 3.13):

classmethod datetime.fromisoformat(date_string):

Return a datetime corresponding to a date_string in any valid ISO 8601 format, with the following exceptions:

1. Time zone offsets may have fractional seconds.
2. The T separator may be replaced by any single unicode character.
3. Fractional hours and minutes are not supported.
4. Reduced precision dates are not currently supported (YYYY-MM, YYYY).
5. Extended date representations are not currently supported (±YYYYYY-MM-DD).
6. Ordinal dates are not currently supported (YYYY-OOO).

Examples:

>>> from datetime import datetime
>>> datetime.fromisoformat('2011-11-04')
datetime.datetime(2011, 11, 4, 0, 0)
>>> datetime.fromisoformat('20111104')
datetime.datetime(2011, 11, 4, 0, 0)
>>> datetime.fromisoformat('2011-11-04T00:05:23')
datetime.datetime(2011, 11, 4, 0, 5, 23)
>>> datetime.fromisoformat('2011-11-04T00:05:23Z')
datetime.datetime(2011, 11, 4, 0, 5, 23, tzinfo=datetime.timezone.utc)
>>> datetime.fromisoformat('20111104T000523')
datetime.datetime(2011, 11, 4, 0, 5, 23)
>>> datetime.fromisoformat('2011-W01-2T00:05:23.283')
datetime.datetime(2011, 1, 4, 0, 5, 23, 283000)
>>> datetime.fromisoformat('2011-11-04 00:05:23.283')
datetime.datetime(2011, 11, 4, 0, 5, 23, 283000)
>>> datetime.fromisoformat('2011-11-04 00:05:23.283+00:00')
datetime.datetime(2011, 11, 4, 0, 5, 23, 283000, tzinfo=datetime.timezone.utc)
>>> datetime.fromisoformat('2011-11-04T00:05:23+04:00')   
datetime.datetime(2011, 11, 4, 0, 5, 23, tzinfo=datetime.timezone(datetime.timedelta(seconds=14400)))

New in version 3.7.

Changed in version 3.11: Previously, this method only supported formats that could be emitted by date.isoformat() or datetime.isoformat().

If you only need dates, and not datetimes, you can use datetime.date.fromisoformat:

>>> from datetime import date
>>> date.fromisoformat("2024-01-31")
datetime.date(2024, 1, 31)

Note in Python 2.6+ and Py3K, the %f character catches microseconds.

>>> datetime.datetime.strptime("2008-09-03T20:56:35.450686Z", "%Y-%m-%dT%H:%M:%S.%fZ")

See issue here

As of Python 3.7, you can basically (caveats below) get away with using datetime.datetime.strptime to parse RFC 3339 datetimes, like this:

from datetime import datetime

def parse_rfc3339(datetime_str: str) -> datetime:
    try:
        return datetime.strptime(datetime_str, "%Y-%m-%dT%H:%M:%S.%f%z")
    except ValueError:
        # Perhaps the datetime has a whole number of seconds with no decimal
        # point. In that case, this will work:
        return datetime.strptime(datetime_str, "%Y-%m-%dT%H:%M:%S%z")

It's a little awkward, since we need to try two different format strings in order to support both datetimes with a fractional number of seconds (like 2022-01-01T12:12:12.123Z) and those without (like 2022-01-01T12:12:12Z), both of which are valid under RFC 3339. But as long as we do that single fiddly bit of logic, this works.

Some caveats to note about this approach:

• It technically doesn't fully support RFC 3339, since RFC 3339 bizarrely lets you use a space instead of a T to separate the date from the time, even though RFC 3339 purports to be a profile of ISO 8601 and ISO 8601 does not allow this. If you want to support this silly quirk of RFC 3339, you could add datetime_str = datetime_str.replace(' ', 'T') to the start of the function.
• My implementation above is slightly more permissive than a strict RFC 3339 parser should be, since it will allow timezone offsets like +0500 without a colon, which RFC 3339 does not support. If you don't merely want to parse known-to-be-RFC-3339 datetimes but also want to rigorously validate that the datetime you're getting is RFC 3339, use another approach or add in your own logic to validate the timezone offset format.
• This function definitely doesn't support all of ISO 8601, which includes a much wider array of formats than RFC 3339. (e.g. 2009-W01-1 is a valid ISO 8601 date.)
• It does not work in Python 3.6 or earlier, since in those old versions the %z specifier only matches timezones offsets like +0500 or -0430 or +0000, not RFC 3339 timezone offsets like +05:00 or -04:30 or Z.

Python >= 3.11

fromisoformat now parses Z directly:

from datetime import datetime

s = "2008-09-03T20:56:35.450686Z"

datetime.fromisoformat(s)
datetime.datetime(2008, 9, 3, 20, 56, 35, 450686, tzinfo=datetime.timezone.utc)

Python 3.7 to 3.10

A simple option from one of the comments: replace 'Z' with '+00:00' - and use fromisoformat:

from datetime import datetime

s = "2008-09-03T20:56:35.450686Z"

datetime.fromisoformat(s.replace('Z', '+00:00'))
# datetime.datetime(2008, 9, 3, 20, 56, 35, 450686, tzinfo=datetime.timezone.utc)

Why prefer fromisoformat?

Although strptime's %z can parse the 'Z' character to UTC, fromisoformat is faster by ~ x40 (or even ~x60 for Python 3.11):

from datetime import datetime
from dateutil import parser

s = "2008-09-03T20:56:35.450686Z"

# Python 3.11+
%timeit datetime.fromisoformat(s)
85.1 ns ± 0.473 ns per loop (mean ± std. dev. of 7 runs, 10,000,000 loops each)

# Python 3.7 to 3.10
%timeit datetime.fromisoformat(s.replace('Z', '+00:00'))
134 ns ± 0.522 ns per loop (mean ± std. dev. of 7 runs, 10,000,000 loops each)

%timeit parser.isoparse(s)
4.09 µs ± 5.2 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops each)

%timeit datetime.strptime(s, '%Y-%m-%dT%H:%M:%S.%f%z')
5 µs ± 9.26 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops each)

%timeit parser.parse(s)
28.5 µs ± 99.2 ns per loop (mean ± std. dev. of 7 runs, 10,000 loops each)

(Python 3.11.3 x64 on GNU/Linux)

See also: A faster strptime

Try the iso8601 module; it does exactly this.

There are several other options mentioned on the WorkingWithTime page on the python.org wiki.

Starting from Python 3.7, strptime supports colon delimiters in UTC offsets (source). So you can then use:

import datetime

def parse_date_string(date_string: str) -> datetime.datetime
    try:
       return datetime.datetime.strptime(date_string, '%Y-%m-%dT%H:%M:%S.%f%z')
    except ValueError:
       return datetime.datetime.strptime(date_string, '%Y-%m-%dT%H:%M:%S%z')

EDIT:

As pointed out by Martijn, if you created the datetime object using isoformat(), you can simply use datetime.fromisoformat().

EDIT 2:

As pointed out by Mark Amery, I added a try..except block to account for missing fractional seconds.

What is the exact error you get? Is it like the following?

>>> datetime.datetime.strptime("2008-08-12T12:20:30.656234Z", "%Y-%m-%dT%H:%M:%S.Z")
ValueError: time data did not match format:  data=2008-08-12T12:20:30.656234Z  fmt=%Y-%m-%dT%H:%M:%S.Z

If yes, you can split your input string on ".", and then add the microseconds to the datetime you got.

Try this:

>>> def gt(dt_str):
        dt, _, us= dt_str.partition(".")
        dt= datetime.datetime.strptime(dt, "%Y-%m-%dT%H:%M:%S")
        us= int(us.rstrip("Z"), 10)
        return dt + datetime.timedelta(microseconds=us)

>>> gt("2008-08-12T12:20:30.656234Z")
datetime.datetime(2008, 8, 12, 12, 20, 30, 656234)

import re
import datetime
s = "2008-09-03T20:56:35.450686Z"
d = datetime.datetime(*map(int, re.split(r'[^\d]', s)[:-1]))

In these days, Arrow also can be used as a third-party solution:

>>> import arrow
>>> date = arrow.get("2008-09-03T20:56:35.450686Z")
>>> date.datetime
datetime.datetime(2008, 9, 3, 20, 56, 35, 450686, tzinfo=tzutc())

Just use the python-dateutil module:

>>> import dateutil.parser as dp
>>> t = '1984-06-02T19:05:00.000Z'
>>> parsed_t = dp.parse(t)
>>> print(parsed_t)
datetime.datetime(1984, 6, 2, 19, 5, tzinfo=tzutc())

Documentation

I have found ciso8601 to be the fastest way to parse ISO 8601 timestamps.

It also has full support for RFC 3339, and a dedicated function for strict parsing RFC 3339 timestamps.

Example usage:

>>> import ciso8601
>>> ciso8601.parse_datetime('2014-01-09T21')
datetime.datetime(2014, 1, 9, 21, 0)
>>> ciso8601.parse_datetime('2014-01-09T21:48:00.921000+05:30')
datetime.datetime(2014, 1, 9, 21, 48, 0, 921000, tzinfo=datetime.timezone(datetime.timedelta(seconds=19800)))
>>> ciso8601.parse_rfc3339('2014-01-09T21:48:00.921000+05:30')
datetime.datetime(2014, 1, 9, 21, 48, 0, 921000, tzinfo=datetime.timezone(datetime.timedelta(seconds=19800)))

The GitHub Repo README shows their speedup versus all of the other libraries listed in the other answers.

My personal project involved a lot of ISO 8601 parsing. It was nice to be able to just switch the call and go faster. :)

Edit: I have since become a maintainer of ciso8601. It's now faster than ever!

If you are working with Django, it provides the dateparse module that accepts a bunch of formats similar to ISO format, including the time zone.

If you are not using Django and you don't want to use one of the other libraries mentioned here, you could probably adapt the Django source code for dateparse to your project.

If you don't want to use dateutil, you can try this function:

def from_utc(utcTime,fmt="%Y-%m-%dT%H:%M:%S.%fZ"):
    """
    Convert UTC time string to time.struct_time
    """
    # change datetime.datetime to time, return time.struct_time type
    return datetime.datetime.strptime(utcTime, fmt)

Test:

from_utc("2007-03-04T21:08:12.123Z")

Result:

datetime.datetime(2007, 3, 4, 21, 8, 12, 123000)

I've coded up a parser for the ISO 8601 standard and put it on GitHub: https://github.com/boxed/iso8601. This implementation supports everything in the specification except for durations, intervals, periodic intervals, and dates outside the supported date range of Python's datetime module.

Tests are included! :P

This works for stdlib on Python 3.2 onwards (assuming all the timestamps are UTC):

from datetime import datetime, timezone, timedelta
datetime.strptime(timestamp, "%Y-%m-%dT%H:%M:%S.%fZ").replace(
    tzinfo=timezone(timedelta(0)))

For example,

>>> datetime.utcnow().replace(tzinfo=timezone(timedelta(0)))
... datetime.datetime(2015, 3, 11, 6, 2, 47, 879129, tzinfo=datetime.timezone.utc)

I'm the author of iso8601utils. It can be found on GitHub or on PyPI. Here's how you can parse your example:

>>> from iso8601utils import parsers
>>> parsers.datetime('2008-09-03T20:56:35.450686Z')
datetime.datetime(2008, 9, 3, 20, 56, 35, 450686)

One straightforward way to convert an ISO 8601-like date string to a UNIX timestamp or datetime.datetime object in all supported Python versions without installing third-party modules is to use the date parser of SQLite.

#!/usr/bin/env python
from __future__ import with_statement, division, print_function
import sqlite3
import datetime

testtimes = [
    "2016-08-25T16:01:26.123456Z",
    "2016-08-25T16:01:29",
]
db = sqlite3.connect(":memory:")
c = db.cursor()
for timestring in testtimes:
    c.execute("SELECT strftime('%s', ?)", (timestring,))
    converted = c.fetchone()[0]
    print("%s is %s after epoch" % (timestring, converted))
    dt = datetime.datetime.fromtimestamp(int(converted))
    print("datetime is %s" % dt)

Output:

2016-08-25T16:01:26.123456Z is 1472140886 after epoch
datetime is 2016-08-25 12:01:26
2016-08-25T16:01:29 is 1472140889 after epoch
datetime is 2016-08-25 12:01:29

An another way is to use specialized parser for ISO-8601 is to use isoparse function of dateutil parser:

from dateutil import parser

date = parser.isoparse("2008-09-03T20:56:35.450686+01:00")
print(date)

Output:

2008-09-03 20:56:35.450686+01:00

This function is also mentioned in the documentation for the standard Python function datetime.fromisoformat:

A more full-featured ISO 8601 parser, dateutil.parser.isoparse is available in the third-party package dateutil.

Django's parse_datetime() function supports dates with UTC offsets:

parse_datetime('2016-08-09T15:12:03.65478Z') =
datetime.datetime(2016, 8, 9, 15, 12, 3, 654780, tzinfo=<UTC>)

So it could be used for parsing ISO 8601 dates in fields within entire project:

from django.utils import formats
from django.forms.fields import DateTimeField
from django.utils.dateparse import parse_datetime

class DateTimeFieldFixed(DateTimeField):
    def strptime(self, value, format):
        if format == 'iso-8601':
            return parse_datetime(value)
        return super().strptime(value, format)

DateTimeField.strptime = DateTimeFieldFixed.strptime
formats.ISO_INPUT_FORMATS['DATETIME_INPUT_FORMATS'].insert(0, 'iso-8601')

If pandas is used anyway, I can recommend Timestamp from pandas. There you can

ts_1 = pd.Timestamp('2020-02-18T04:27:58.000Z')    
ts_2 = pd.Timestamp('2020-02-18T04:27:58.000')

Rant: It is just unbelievable that we still need to worry about things like date string parsing in 2021.

datetime.fromisoformat() is improved in Python 3.11 to parse most ISO 8601 formats

datetime.fromisoformat() can now be used to parse most ISO 8601 formats, barring only those that support fractional hours and minutes. Previously, this method only supported formats that could be emitted by datetime.isoformat().

>>> from datetime import datetime
>>> datetime.fromisoformat('2011-11-04T00:05:23Z')
datetime.datetime(2011, 11, 4, 0, 5, 23, tzinfo=datetime.timezone.utc)
>>> datetime.fromisoformat('20111104T000523')
datetime.datetime(2011, 11, 4, 0, 5, 23)
>>> datetime.fromisoformat('2011-W01-2T00:05:23.283')
datetime.datetime(2011, 1, 4, 0, 5, 23, 283000)

Because ISO 8601 allows many variations of optional colons and dashes being present, basically CCYY-MM-DDThh:mm:ss[Z|(+|-)hh:mm]. If you want to use strptime, you need to strip out those variations first.

The goal is to generate a utc datetime object.

datetime.datetime.strptime(timestamp.translate(None, ':-'), "%Y%m%dT%H%M%S.%fZ")

import re
# this regex removes all colons and all 
# dashes EXCEPT for the dash indicating + or - utc offset for the timezone
conformed_timestamp = re.sub(r"[:]|([-](?!((\d{2}[:]\d{2})|(\d{4}))$))", '', timestamp)
datetime.datetime.strptime(conformed_timestamp, "%Y%m%dT%H%M%S.%f%z" )

import re
import datetime

# this regex removes all colons and all 
# dashes EXCEPT for the dash indicating + or - utc offset for the timezone
conformed_timestamp = re.sub(r"[:]|([-](?!((\d{2}[:]\d{2})|(\d{4}))$))", '', timestamp)

# split on the offset to remove it. use a capture group to keep the delimiter
split_timestamp = re.split(r"[+|-]",conformed_timestamp)
main_timestamp = split_timestamp[0]
if len(split_timestamp) == 3:
    sign = split_timestamp[1]
    offset = split_timestamp[2]
else:
    sign = None
    offset = None

# generate the datetime object without the offset at UTC time
output_datetime = datetime.datetime.strptime(main_timestamp +"Z", "%Y%m%dT%H%M%S.%fZ" )
if offset:
    # create timedelta based on offset
    offset_delta = datetime.timedelta(hours=int(sign+offset[:-2]), minutes=int(sign+offset[-2:]))
    # offset datetime with timedelta
    output_datetime = output_datetime + offset_delta

Nowadays there's Maya: Datetimes for Humans™, from the author of the popular Requests: HTTP for Humans™ package:

>>> import maya
>>> str = '2008-09-03T20:56:35.450686Z'
>>> maya.MayaDT.from_rfc3339(str).datetime()
datetime.datetime(2008, 9, 3, 20, 56, 35, 450686, tzinfo=<UTC>)

The python-dateutil will throw an exception if parsing invalid date strings, so you may want to catch the exception.

from dateutil import parser
ds = '2012-60-31'
try:
  dt = parser.parse(ds)
except ValueError, e:
  print '"%s" is an invalid date' % ds

For something that works with the 2.X standard library try:

calendar.timegm(time.strptime(date.split(".")[0]+"UTC", "%Y-%m-%dT%H:%M:%S%Z"))

calendar.timegm is the missing gm version of time.mktime.

Thanks to great Mark Amery's answer I devised function to account for all possible ISO formats of datetime:

class FixedOffset(tzinfo):
    """Fixed offset in minutes: `time = utc_time + utc_offset`."""
    def __init__(self, offset):
        self.__offset = timedelta(minutes=offset)
        hours, minutes = divmod(offset, 60)
        #NOTE: the last part is to remind about deprecated POSIX GMT+h timezones
        #  that have the opposite sign in the name;
        #  the corresponding numeric value is not used e.g., no minutes
        self.__name = '<%+03d%02d>%+d' % (hours, minutes, -hours)
    def utcoffset(self, dt=None):
        return self.__offset
    def tzname(self, dt=None):
        return self.__name
    def dst(self, dt=None):
        return timedelta(0)
    def __repr__(self):
        return 'FixedOffset(%d)' % (self.utcoffset().total_seconds() / 60)
    def __getinitargs__(self):
        return (self.__offset.total_seconds()/60,)

def parse_isoformat_datetime(isodatetime):
    try:
        return datetime.strptime(isodatetime, '%Y-%m-%dT%H:%M:%S.%f')
    except ValueError:
        pass
    try:
        return datetime.strptime(isodatetime, '%Y-%m-%dT%H:%M:%S')
    except ValueError:
        pass
    pat = r'(.*?[+-]\d{2}):(\d{2})'
    temp = re.sub(pat, r'\1\2', isodatetime)
    naive_date_str = temp[:-5]
    offset_str = temp[-5:]
    naive_dt = datetime.strptime(naive_date_str, '%Y-%m-%dT%H:%M:%S.%f')
    offset = int(offset_str[-4:-2])*60 + int(offset_str[-2:])
    if offset_str[0] == "-":
        offset = -offset
    return naive_dt.replace(tzinfo=FixedOffset(offset))

Since I never found a valid python implementation that is able to parse all kind of unusual date time format like

• 2020-12-31T16:20:00.100200300Z (nano seconds)
• 2020-12-31T16:20:00.1002003Z (shortened nano seconds)
• 2020-12-31T16:20:00.100200Z (micro seconds)
• 2020-12-31T16:20:00.1002Z (shortened micro seconds)
• 2020-12-31T16:20:00.100Z (milli seconds)
• 2020-12-31T16:20:00.1Z (shortened milli seconds)
• 2020-12-31T16:20:00Z (seconds)

and all kind of time zone format like:

• 2020-12-31T16:20:00Z (UTC)
• 2020-12-31T16:20:00+0000 (standard TZ)
• 2020-12-31T16:20:00+00:00 (non-standard TZ)

I finally wrote this method (that could certainly be improved):

def parse_datetime(str_time: str) -> datetime:
    """
    parse date, ignoring nanoseconds
    """
    # length can be variable (truncated when last digits are 0)
    try:
        z_index = str_time.index('Z')
    except ValueError:
        z_index = str_time.index('+')

    # standardize nanoseconds / milliseconds / seconds format
    if z_index >= 26:
        # remove nanoseconds
        str_time = str_time[0:26] + str_time[z_index:]
        z_index = 26
    elif z_index == 19:
        # add milliseconds
        str_time = str_time[0:19] + ".000" + str_time[z_index:]
        z_index = 23

    # convert timezone format
    if str_time[z_index] == '+':
        # convert +02:00 to +0200, to match strptime '%f'
        str_time = str_time[0:z_index] + str_time[z_index:].replace(':', '')
    elif str_time[-1] == 'Z':
        # add explicit UTC timezone, to make strptime happy
        str_time = str_time[0:z_index] + '+0000'
    return datetime.strptime(str_time, '%Y-%m-%dT%H:%M:%S.%f%z')

Initially I tried with:

from operator import neg, pos
from time import strptime, mktime
from datetime import datetime, tzinfo, timedelta

class MyUTCOffsetTimezone(tzinfo):
    @staticmethod
    def with_offset(offset_no_signal, signal):  # type: (str, str) -> MyUTCOffsetTimezone
        return MyUTCOffsetTimezone((pos if signal == '+' else neg)(
            (datetime.strptime(offset_no_signal, '%H:%M') - datetime(1900, 1, 1))
          .total_seconds()))

    def __init__(self, offset, name=None):
        self.offset = timedelta(seconds=offset)
        self.name = name or self.__class__.__name__

    def utcoffset(self, dt):
        return self.offset

    def tzname(self, dt):
        return self.name

    def dst(self, dt):
        return timedelta(0)


def to_datetime_tz(dt):  # type: (str) -> datetime
    fmt = '%Y-%m-%dT%H:%M:%S.%f'
    if dt[-6] in frozenset(('+', '-')):
        dt, sign, offset = strptime(dt[:-6], fmt), dt[-6], dt[-5:]
        return datetime.fromtimestamp(mktime(dt),
                                      tz=MyUTCOffsetTimezone.with_offset(offset, sign))
    elif dt[-1] == 'Z':
        return datetime.strptime(dt, fmt + 'Z')
    return datetime.strptime(dt, fmt)

But that didn't work on negative timezones. This however I got working fine, in Python 3.7.3:

from datetime import datetime


def to_datetime_tz(dt):  # type: (str) -> datetime
    fmt = '%Y-%m-%dT%H:%M:%S.%f'
    if dt[-6] in frozenset(('+', '-')):
        return datetime.strptime(dt, fmt + '%z')
    elif dt[-1] == 'Z':
        return datetime.strptime(dt, fmt + 'Z')
    return datetime.strptime(dt, fmt)

Some tests, note that the out only differs by precision of microseconds. Got to 6 digits of precision on my machine, but YMMV:

for dt_in, dt_out in (
        ('2019-03-11T08:00:00.000Z', '2019-03-11T08:00:00'),
        ('2019-03-11T08:00:00.000+11:00', '2019-03-11T08:00:00+11:00'),
        ('2019-03-11T08:00:00.000-11:00', '2019-03-11T08:00:00-11:00')
    ):
    isoformat = to_datetime_tz(dt_in).isoformat()
    assert isoformat == dt_out, '{} != {}'.format(isoformat, dt_out)