ValueError: Unknown string format in Python?

Question

I'm trying to parse a basic iso formatted datetime string in Python, but I'm having a hard time doing that. Consider the following example:

>>> import json
>>> from datetime import datetime, date
>>> import dateutil.parser
>>> date_handler = lambda obj: obj.isoformat()
>>> the_date = json.dumps(datetime.now(), default=date_handler)
>>> print the_date
"2017-02-18T22:14:09.915727"
>>> print dateutil.parser.parse(the_date)
Traceback (most recent call last):
  File "<input>", line 1, in <module>
    print dateutil.parser.parse(the_date)
  File "/usr/local/lib/python2.7/site-packages/dateutil/parser.py", line 1168, in parse
    return DEFAULTPARSER.parse(timestr, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/dateutil/parser.py", line 559, in parse
    raise ValueError("Unknown string format")
ValueError: Unknown string format

I've also tried parsing this using the regular strptime:

>>> print datetime.strptime(the_date, '%Y-%m-%dT%H:%M:%S')
# removed rest of the error output
ValueError: time data '"2017-02-18T22:11:58.125703"' does not match format '%Y-%m-%dT%H:%M:%S'
>>> print datetime.strptime(the_date, '%Y-%m-%dT%H:%M:%S.%f')
# removed rest of the error output
ValueError: time data '"2017-02-18T22:11:58.125703"' does not match format '%Y-%m-%dT%H:%M:%S.%f'

Does anybody know how on earth I can parse this fairly simple datetime format?

Why did you use json.dumps on it? If you have JSON, parse it before parsing the date. — Ry-
– Ry- ♦, Commented Feb 18, 2017 at 21:19

Jean-François Fabre · Accepted Answer · 2017-02-18 21:18:51Z

6

note the error message:

ValueError: time data '"2017-02-18T22:11:58.125703"'

There are single quotes + double quotes which means that the string actually contains double quotes. That's because json serialization adds double quotes to strings.

you may want to strip the quotes around your string:

datetime.strptime(the_date.strip('"'), '%Y-%m-%dT%H:%M:%S.%f')

or, maybe less "hacky", de-serialize using json.loads:

datetime.strptime(json.loads(the_date), '%Y-%m-%dT%H:%M:%S.%f')

answered Feb 18, 2017 at 21:18

Jean-François Fabre♦

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1 Comment

kramer65 Over a year ago

Ah, I overlooked that. Thanks!

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