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Error while using datetime.strptime to convert a string to datetime

I want to convert a string in the following format to a datetime object in Python.
'2019-11-08T13:22:19.173700864-05:00'
I tried to use:
obj = datetime.strptime('2019-11-08T13:22:19.173700864-05:00', '%Y-%m-%dT%H:%M:%S.%f000%z')
I got an error message. It seems %f000 is not the correct way to convert 9-digit after the decimal point. And it seems I am also using %z in the wrong way.
What is the correct way to do this? Thanks.

How to require a timestamp to be zero-padded during validation in Python?

I'm trying to validate a string that's supposed to contain a timestamp in the format of ISO 8601 (commonly used in JSON).
Python's strptime seems to be very forgiving when it comes to validating zero-padding, see code example below (note that the hour is missing a leading zero):
>>> import datetime
>>> s = '1985-08-23T3:00:00.000'
>>> datetime.datetime.strptime(s, '%Y-%m-%dT%H:%M:%S.%f')
datetime.datetime(1985, 8, 23, 3, 0)
It gracefully accepts a string that's not zero-padded for the hour for example, and doesn't throw a ValueError exception as I would expect.
Is there any way to enforce strptime to validate that it's zero-padded? Or is there any other built-in function in the standard libs of Python that does?
I would like to avoid writing my own regexp for this.

There is already an answer that parsing ISO8601 or RFC3339 date/time with Python strptime() is impossible: How to parse an ISO 8601-formatted date?
So, to answer you question, no there is no way in the standard Python library to reliable parse such a date.
Regarding the regex suggestions, a date string like
2020-14-32T45:33:44.123
would result in a valid date. There are lots of Python modules (if you search for "iso8601" on https://pypi.python.org), but building a complete ISO8601 Validator would require things like leap seconds, the list of possible time zone offset values and many more.

To enforce strptime to validate leading zeros for you you'll have to add your own literals to Python's _strptime._TimeRE_cache. The solution is very hacky, most likely not very portable, and requires writing a RegEx - although only for the hour part of a timestamp.
Another solution to the problem would be to write your own function that uses strptime and also converts the parsed date back to a string and compares the two strings. This solution is portable, but it lacks for the clear error messages - you won't be able to distinguish between missing leading zeros in hours, minutes, seconds.

You said you want to avoid a regex, but this is actually the type of problem where a regex is appropriate. As you discovered, strptime is very flexible about the input it will accept. However, the regex for this problem is relatively easy to compose:
import re
date_pattern = re.compile(r'\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.\d{3}')
s_list = [
'1985-08-23T3:00:00.000',
'1985-08-23T03:00:00.000'
]
for s in s_list:
if date_pattern.match(s):
print "%s is valid" % s
else:
print "%s is invalid" % s
Output
1985-08-23T3:00:00.000 is invalid
1985-08-23T03:00:00.000 is valid
Try it on repl.it

The only thing I can think of outside of messing with Python internals is to test for the validity of the format by knowing what you are looking for.
So, if I garner it right, the format is '%Y-%m-%dT%H:%M:%S.%f' and should be zero padded.
Then, you know the exact length of the string you are looking for and reproduce the intended result..
import datetime
s = '1985-08-23T3:00:00.000'
stripped = datetime.datetime.strptime(s, '%Y-%m-%dT%H:%M:%S.%f')
try:
assert len(s) == 23
except AssertionError:
raise ValueError("time data '{}' does not match format '%Y-%m-%dT%H:%M:%S.%f".format(s))
else:
print(stripped) #just for good measure
>>ValueError: time data '1985-08-23T3:00:00.000' does not match format '%Y-%m-%dT%H:%M:%S.%f

Python - Getting the date format [duplicate]

This question already has answers here:
How to determine appropriate strftime format from a date string?
(4 answers)
Closed 5 years ago.
I'm getting a date as a string, then I'm parsing it to datetime object.
Is there any way to check what's is the date format of the object?
Let's say that this is the object that I'm creating:
modified_date = parser.parse("2015-09-01T12:34:15.601+03:00")
How can i print or get the exact date format of this object, i need this in order to verify that it's in the correct format, so I'll be able to to make a diff of today's date and the given date.

I had a look in the source code and, unfortunately, python-dateutil doesn't expose the format. In fact it doesn't even generate a guess for the format at all, it just goes ahead and parses - the code is like a big nested spaghetti of conditionals.
You could have a look at dateinfer which looks to be what you're searching for, but these are unrelated libraries so there is no guarantee at all that python-dateutil will parse with the same format that dateinfer suggests.
>>> from dateinfer import infer
>>> s = "2015-09-01T12:34:15.601+03:00"
>>> infer([s])
'%Y-%d-%mT%I:%M:%S.601+%m:%d'
Look at that .601. Close but not cigar. I think it has probably also mixed up the month and the day. You might get better results by giving it more than one date string to base the guess upon.

i need this in order to verify that it's in the correct format
If you know the expected time format (or a set of valid time formats) then you could just parse the input using it: if it succeeds then the time format is valid (the usual EAFP approach in Python):
for date_format in valid_date_formats:
try:
return datetime.strptime(date_string, date_format), date_format
except ValueError: # wrong date format
pass # try the next format
raise ValueError("{date_string} is not in the correct format. "
"valid formats: {valid_date_formats}".format(**vars()))
Here's a complete code example (in Russian -- ignore the text, look at the code).
If there are many valid date formats then to improve time performance you might want to combine them into a single regular expression or convert the regex to a deterministic or non-deterministic finite-state automaton (DFA or NFA).
In general, if you need to extract dates from a larger text that is too varied to create parsing rules manually; consider machine learning solutions e.g., a NER system such as webstruct (for html input).

Checking if a date string is in UTC format

I have a date string like "2011-11-06 14:00:00+00:00". Is there a way to check if this is in UTC format or not ?. I tried to convert the above string to a datetime object using utc = datetime.strptime('2011-11-06 14:00:00+00:00','%Y-%m-%d %H:%M%S+%z) so that i can compare it with pytz.utc, but i get 'ValueError: 'z' is a bad directive in format '%Y-%m-%d %H:%M%S+%z'
How to check if the date string is in UTC ?. Some example would be really appreciated.
Thank You

A simple regular expression will do:
>>> import re
>>> RE = re.compile(r'^\d{4}-\d{2}-\d{2}[ T]\d{2}:\d{2}:\d{2}[+-]\d{2}:\d{2}$')
>>> bool(RE.search('2011-11-06 14:00:00+00:00'))
True

By 'in UTC format' do you actually mean ISO-8601?. This is a pretty common question.

The problem with your format string is that strptime just passes the job of parsing time strings on to c's strptime, and different flavors of c accept different directives. In your case (and mine, it seems), the %z directive is not accepted.
There's some ambiguity in the doc pages about this. The datetime.datetime.strptime docs point to the format specification for time.strptime which doesn't contain a lower-case %z directive, and indicates that
Additional directives may be supported on certain platforms, but only the ones listed here have a meaning standardized by ANSI C.
But then it also points here which does contain a lower-case %z, but reiterates that
The full set of format codes supported varies across platforms, because Python calls the platform C library’s strftime() function, and platform variations are common.
There's also a bug report about this issue.

Parsing datetime strings with microseconds in Python 2.5

I have a text file with a lot of datetime strings in isoformat. The strings are similar to this:
'2009-02-10 16:06:52.598800'
These strings were generated using str(datetime_object). The problem is that, for some reason, str(datetime_object) generates a different format when the datetime object has microseconds set to zero and some strings look like this:
'2009-02-10 16:06:52'
How can I parse these strings and convert them into a datetime object?
It's very important to get all the data in the object, including microseconds.
NOTE: I have to use Python 2.5, the format directive %f for microseconds doesn't exist in 2.5.

Alternatively:
from datetime import datetime
def str2datetime(s):
parts = s.split('.')
dt = datetime.strptime(parts[0], "%Y-%m-%d %H:%M:%S")
return dt.replace(microsecond=int(parts[1]))
Using strptime itself to parse the date/time string (so no need to think up corner cases for a regex).

Use the dateutil module. It supports a much wider range of date and time formats than the built in Python ones.
You'll need to easy_install dateutil for the following code to work:
from dateutil.parser import parser
p = parser()
datetime_with_microseconds = p.parse('2009-02-10 16:06:52.598800')
print datetime_with_microseconds.microsecond
results in:
598799

Someone has already filed a bug with this issue: Issue 1982. Since you need this to work with python 2.5 you must parse the value manualy and then manipulate the datetime object.

It might not be the best solution, but you can use a regular expression:
m = re.match(r'(\d{4})-(\d{2})-(\d{2}) (\d{2}):(\d{2}):(\d{2})(?:\.(\d{6}))?', datestr)
dt = datetime.datetime(*[int(x) for x in m.groups() if x])