How do I parse an ISO 8601-formatted date?

Question

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?

Answer 1

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 fromisoformat is deliberately not. Please see the latter function's docs for this cautionary caveat. (See this answer).

Answer 2

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 one of the formats emitted by date.isoformat() and datetime.isoformat().

Specifically, this function supports strings in the format(s):

YYYY-MM-DD[*HH[:MM[:SS[.mmm[mmm]]]][+HH:MM[:SS[.ffffff]]]]

where * can match any single character.

Caution: This does not support parsing arbitrary ISO 8601 strings - it is only intended as the inverse operation of datetime.isoformat().

Examples:

>>> from datetime import datetime >>> datetime.fromisoformat('2011-11-04') datetime.datetime(2011, 11, 4, 0, 0) 

…

Be sure to read the caution from the docs!