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redefinition of group name 'H' as group 7; was group 4 at position 169 [duplicate]

I need to parse RFC 3339 strings like "2008-09-03T20:56:35.450686Z" into Python's datetime type.
I have found strptime in the Python standard library, but it is not very convenient.
What is the best way to do this?

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).

The datetime standard library has, since Python 3.7, a function for inverting datetime.isoformat().
classmethod datetime.fromisoformat(date_string):
Return a datetime corresponding to a date_string in any valid ISO 8601 format, with the following exceptions:
Time zone offsets may have fractional seconds.
The T separator may be replaced by any single unicode character.
Ordinal dates are not currently supported.
Fractional hours and minutes are not supported.
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().
Be sure to read the caution from the docs if you haven't upgraded to Python 3.11 yet!

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.

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.

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 (see also: A faster strptime):
%timeit datetime.fromisoformat(s.replace('Z', '+00:00'))
388 ns ± 48.3 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
%timeit dateutil.parser.isoparse(s)
11 µs ± 1.05 µs per loop (mean ± std. dev. of 7 runs, 100000 loops each)
%timeit datetime.strptime(s, '%Y-%m-%dT%H:%M:%S.%f%z')
15.8 µs ± 1.32 µs per loop (mean ± std. dev. of 7 runs, 100000 loops each)
%timeit dateutil.parser.parse(s)
87.8 µs ± 8.54 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)
(Python 3.9.12 x64 on Windows 10)

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.

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.
If you just want a basic case that work for UTC with the Z suffix like 2016-06-29T19:36:29.3453Z:
datetime.datetime.strptime(timestamp.translate(None, ':-'), "%Y%m%dT%H%M%S.%fZ")
If you want to handle timezone offsets like 2016-06-29T19:36:29.3453-0400 or 2008-09-03T20:56:35.450686+05:00 use the following. These will convert all variations into something without variable delimiters like 20080903T205635.450686+0500 making it more consistent/easier to parse.
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}))$))", '', timestamp)
datetime.datetime.strptime(conformed_timestamp, "%Y%m%dT%H%M%S.%f%z" )
If your system does not support the %z strptime directive (you see something like ValueError: 'z' is a bad directive in format '%Y%m%dT%H%M%S.%f%z') then you need to manually offset the time from Z (UTC). Note %z may not work on your system in python versions < 3 as it depended on the c library support which varies across system/python build type (i.e. Jython, Cython, etc.).
import re
import datetime
# this regex removes all colons and all
# dashes EXCEPT for the dash indicating + or - utc offset for the timezone
conformed_timestamp = re.sub(r"[:]|([-](?!((\d{2}[:]\d{2})|(\d{4}))$))", '', 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))

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)

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)

def parseISO8601DateTime(datetimeStr):
import time
from datetime import datetime, timedelta
def log_date_string(when):
gmt = time.gmtime(when)
if time.daylight and gmt[8]:
tz = time.altzone
else:
tz = time.timezone
if tz > 0:
neg = 1
else:
neg = 0
tz = -tz
h, rem = divmod(tz, 3600)
m, rem = divmod(rem, 60)
if neg:
offset = '-%02d%02d' % (h, m)
else:
offset = '+%02d%02d' % (h, m)
return time.strftime('%d/%b/%Y:%H:%M:%S ', gmt) + offset
dt = datetime.strptime(datetimeStr, '%Y-%m-%dT%H:%M:%S.%fZ')
timestamp = dt.timestamp()
return dt + timedelta(hours=dt.hour-time.gmtime(timestamp).tm_hour)
Note that we should look if the string doesn't ends with Z, we could parse using %z.

Incorrect datetime format 'YYYY-MM-DDThh:mm:ss.sssZ' [duplicate]

I need to parse RFC 3339 strings like "2008-09-03T20:56:35.450686Z" into Python's datetime type.
I have found strptime in the Python standard library, but it is not very convenient.
What is the best way to do this?

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).

The datetime standard library has, since Python 3.7, a function for inverting datetime.isoformat().
classmethod datetime.fromisoformat(date_string):
Return a datetime corresponding to a date_string in any valid ISO 8601 format, with the following exceptions:
Time zone offsets may have fractional seconds.
The T separator may be replaced by any single unicode character.
Ordinal dates are not currently supported.
Fractional hours and minutes are not supported.
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().
Be sure to read the caution from the docs if you haven't upgraded to Python 3.11 yet!

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.

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.

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 (see also: A faster strptime):
%timeit datetime.fromisoformat(s.replace('Z', '+00:00'))
388 ns ± 48.3 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
%timeit dateutil.parser.isoparse(s)
11 µs ± 1.05 µs per loop (mean ± std. dev. of 7 runs, 100000 loops each)
%timeit datetime.strptime(s, '%Y-%m-%dT%H:%M:%S.%f%z')
15.8 µs ± 1.32 µs per loop (mean ± std. dev. of 7 runs, 100000 loops each)
%timeit dateutil.parser.parse(s)
87.8 µs ± 8.54 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)
(Python 3.9.12 x64 on Windows 10)

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.

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.
If you just want a basic case that work for UTC with the Z suffix like 2016-06-29T19:36:29.3453Z:
datetime.datetime.strptime(timestamp.translate(None, ':-'), "%Y%m%dT%H%M%S.%fZ")
If you want to handle timezone offsets like 2016-06-29T19:36:29.3453-0400 or 2008-09-03T20:56:35.450686+05:00 use the following. These will convert all variations into something without variable delimiters like 20080903T205635.450686+0500 making it more consistent/easier to parse.
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}))$))", '', timestamp)
datetime.datetime.strptime(conformed_timestamp, "%Y%m%dT%H%M%S.%f%z" )
If your system does not support the %z strptime directive (you see something like ValueError: 'z' is a bad directive in format '%Y%m%dT%H%M%S.%f%z') then you need to manually offset the time from Z (UTC). Note %z may not work on your system in python versions < 3 as it depended on the c library support which varies across system/python build type (i.e. Jython, Cython, etc.).
import re
import datetime
# this regex removes all colons and all
# dashes EXCEPT for the dash indicating + or - utc offset for the timezone
conformed_timestamp = re.sub(r"[:]|([-](?!((\d{2}[:]\d{2})|(\d{4}))$))", '', 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))

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)

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)

def parseISO8601DateTime(datetimeStr):
import time
from datetime import datetime, timedelta
def log_date_string(when):
gmt = time.gmtime(when)
if time.daylight and gmt[8]:
tz = time.altzone
else:
tz = time.timezone
if tz > 0:
neg = 1
else:
neg = 0
tz = -tz
h, rem = divmod(tz, 3600)
m, rem = divmod(rem, 60)
if neg:
offset = '-%02d%02d' % (h, m)
else:
offset = '+%02d%02d' % (h, m)
return time.strftime('%d/%b/%Y:%H:%M:%S ', gmt) + offset
dt = datetime.strptime(datetimeStr, '%Y-%m-%dT%H:%M:%S.%fZ')
timestamp = dt.timestamp()
return dt + timedelta(hours=dt.hour-time.gmtime(timestamp).tm_hour)
Note that we should look if the string doesn't ends with Z, we could parse using %z.

Python: Issue converting ISO 8601 to datetime object [duplicate]

I need to parse RFC 3339 strings like "2008-09-03T20:56:35.450686Z" into Python's datetime type.
I have found strptime in the Python standard library, but it is not very convenient.
What is the best way to do this?

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).

The datetime standard library has, since Python 3.7, a function for inverting datetime.isoformat().
classmethod datetime.fromisoformat(date_string):
Return a datetime corresponding to a date_string in any valid ISO 8601 format, with the following exceptions:
Time zone offsets may have fractional seconds.
The T separator may be replaced by any single unicode character.
Ordinal dates are not currently supported.
Fractional hours and minutes are not supported.
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().
Be sure to read the caution from the docs if you haven't upgraded to Python 3.11 yet!

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.

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.

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 (see also: A faster strptime):
%timeit datetime.fromisoformat(s.replace('Z', '+00:00'))
388 ns ± 48.3 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
%timeit dateutil.parser.isoparse(s)
11 µs ± 1.05 µs per loop (mean ± std. dev. of 7 runs, 100000 loops each)
%timeit datetime.strptime(s, '%Y-%m-%dT%H:%M:%S.%f%z')
15.8 µs ± 1.32 µs per loop (mean ± std. dev. of 7 runs, 100000 loops each)
%timeit dateutil.parser.parse(s)
87.8 µs ± 8.54 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)
(Python 3.9.12 x64 on Windows 10)

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.

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.
If you just want a basic case that work for UTC with the Z suffix like 2016-06-29T19:36:29.3453Z:
datetime.datetime.strptime(timestamp.translate(None, ':-'), "%Y%m%dT%H%M%S.%fZ")
If you want to handle timezone offsets like 2016-06-29T19:36:29.3453-0400 or 2008-09-03T20:56:35.450686+05:00 use the following. These will convert all variations into something without variable delimiters like 20080903T205635.450686+0500 making it more consistent/easier to parse.
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}))$))", '', timestamp)
datetime.datetime.strptime(conformed_timestamp, "%Y%m%dT%H%M%S.%f%z" )
If your system does not support the %z strptime directive (you see something like ValueError: 'z' is a bad directive in format '%Y%m%dT%H%M%S.%f%z') then you need to manually offset the time from Z (UTC). Note %z may not work on your system in python versions < 3 as it depended on the c library support which varies across system/python build type (i.e. Jython, Cython, etc.).
import re
import datetime
# this regex removes all colons and all
# dashes EXCEPT for the dash indicating + or - utc offset for the timezone
conformed_timestamp = re.sub(r"[:]|([-](?!((\d{2}[:]\d{2})|(\d{4}))$))", '', 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))

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)

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)

def parseISO8601DateTime(datetimeStr):
import time
from datetime import datetime, timedelta
def log_date_string(when):
gmt = time.gmtime(when)
if time.daylight and gmt[8]:
tz = time.altzone
else:
tz = time.timezone
if tz > 0:
neg = 1
else:
neg = 0
tz = -tz
h, rem = divmod(tz, 3600)
m, rem = divmod(rem, 60)
if neg:
offset = '-%02d%02d' % (h, m)
else:
offset = '+%02d%02d' % (h, m)
return time.strftime('%d/%b/%Y:%H:%M:%S ', gmt) + offset
dt = datetime.strptime(datetimeStr, '%Y-%m-%dT%H:%M:%S.%fZ')
timestamp = dt.timestamp()
return dt + timedelta(hours=dt.hour-time.gmtime(timestamp).tm_hour)
Note that we should look if the string doesn't ends with Z, we could parse using %z.

Is there a wildcard format directive for strptime?

I'm using strptime like this:
import time
time.strptime("+10:00","+%H:%M")
but "+10:00" could also be "-10:00" (timezone offset from UTC) which would break the above command. I could use
time.strptime("+10:00"[1:],"%H:%M")
but ideally I'd find it more readable to use a wildcard in front of the format code.
Does such a wildcard operator exist for Python's strptime / strftime?

There is no wildcard operator. The list of format directives supported by strptime is in the docs.
What you're looking for is the %z format directive, which supports a representation of the timezone of the form +HHMM or -HHMM. While it has been supported by datetime.strftime for some time, it is only supported in strptime starting in Python 3.2.
On Python 2, the best way to handle this is probably to use datetime.datetime.strptime, manually handle the negative offset, and get a datetime.timedelta:
import datetime
tz = "+10:00"
def tz_to_timedelta(tz):
min = datetime.datetime.strptime('', '')
try:
return -(datetime.datetime.strptime(tz,"-%H:%M") - min)
except ValueError:
return datetime.datetime.strptime(tz,"+%H:%M") - min
print tz_to_timedelta(tz)
In Python 3.2, remove the : and use %z:
import time
tz = "+10:00"
tz_toconvert = tz[:3] + tz[4:]
tz_struct_time = time.strptime(tz_toconvert, "%z")

We developed datetime-glob to parse date/times from a list of files generated by a consistent date/time formatting. From the module's documentation:
>>> import datetime_glob
>>> matcher = datetime_glob.Matcher(
pattern='/some/path/*%Y-%m-%dT%H-%M-%SZ.jpg')
>>> matcher.match(path='/some/path/some-text2016-07-03T21-22-23Z.jpg')
datetime_glob.Match(year = 2016, month = 7, day = 3,
hour = 21, minute = 22, second = 23, microsecond = None)
>>> match.as_datetime()
datetime.datetime(2016, 7, 3, 21, 22, 23)

How do I parse an ISO 8601-formatted date?

I need to parse RFC 3339 strings like "2008-09-03T20:56:35.450686Z" into Python's datetime type.
I have found strptime in the Python standard library, but it is not very convenient.
What is the best way to do this?

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).

The datetime standard library has, since Python 3.7, a function for inverting datetime.isoformat().
classmethod datetime.fromisoformat(date_string):
Return a datetime corresponding to a date_string in any valid ISO 8601 format, with the following exceptions:
Time zone offsets may have fractional seconds.
The T separator may be replaced by any single unicode character.
Ordinal dates are not currently supported.
Fractional hours and minutes are not supported.
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().
Be sure to read the caution from the docs if you haven't upgraded to Python 3.11 yet!

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.

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.

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 (see also: A faster strptime):
%timeit datetime.fromisoformat(s.replace('Z', '+00:00'))
388 ns ± 48.3 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
%timeit dateutil.parser.isoparse(s)
11 µs ± 1.05 µs per loop (mean ± std. dev. of 7 runs, 100000 loops each)
%timeit datetime.strptime(s, '%Y-%m-%dT%H:%M:%S.%f%z')
15.8 µs ± 1.32 µs per loop (mean ± std. dev. of 7 runs, 100000 loops each)
%timeit dateutil.parser.parse(s)
87.8 µs ± 8.54 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)
(Python 3.9.12 x64 on Windows 10)

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.

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.
If you just want a basic case that work for UTC with the Z suffix like 2016-06-29T19:36:29.3453Z:
datetime.datetime.strptime(timestamp.translate(None, ':-'), "%Y%m%dT%H%M%S.%fZ")
If you want to handle timezone offsets like 2016-06-29T19:36:29.3453-0400 or 2008-09-03T20:56:35.450686+05:00 use the following. These will convert all variations into something without variable delimiters like 20080903T205635.450686+0500 making it more consistent/easier to parse.
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}))$))", '', timestamp)
datetime.datetime.strptime(conformed_timestamp, "%Y%m%dT%H%M%S.%f%z" )
If your system does not support the %z strptime directive (you see something like ValueError: 'z' is a bad directive in format '%Y%m%dT%H%M%S.%f%z') then you need to manually offset the time from Z (UTC). Note %z may not work on your system in python versions < 3 as it depended on the c library support which varies across system/python build type (i.e. Jython, Cython, etc.).
import re
import datetime
# this regex removes all colons and all
# dashes EXCEPT for the dash indicating + or - utc offset for the timezone
conformed_timestamp = re.sub(r"[:]|([-](?!((\d{2}[:]\d{2})|(\d{4}))$))", '', 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))

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)

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)

def parseISO8601DateTime(datetimeStr):
import time
from datetime import datetime, timedelta
def log_date_string(when):
gmt = time.gmtime(when)
if time.daylight and gmt[8]:
tz = time.altzone
else:
tz = time.timezone
if tz > 0:
neg = 1
else:
neg = 0
tz = -tz
h, rem = divmod(tz, 3600)
m, rem = divmod(rem, 60)
if neg:
offset = '-%02d%02d' % (h, m)
else:
offset = '+%02d%02d' % (h, m)
return time.strftime('%d/%b/%Y:%H:%M:%S ', gmt) + offset
dt = datetime.strptime(datetimeStr, '%Y-%m-%dT%H:%M:%S.%fZ')
timestamp = dt.timestamp()
return dt + timedelta(hours=dt.hour-time.gmtime(timestamp).tm_hour)
Note that we should look if the string doesn't ends with Z, we could parse using %z.