[New-bugs-announce] [issue42371] Missing colon in timezone suffix raises ValueError

[Bengt Lüers]

New submission from Bengt Lüers <bengt.lueers at gmail.com>:

I am trying to parse ISO8601-formatted datetime strings with timezones.

This works fine when there is a colon separating the hour and minute digits:

>>> import datetime
>>> datetime.datetime.fromisoformat('2020-11-16T11:00:00+00:00')
>>> datetime.datetime(2020, 11, 16, 11, 0, tzinfo=datetime.timezone.utc)

However this fails when there is no colon between the hour and the minute digits:

>>> import datetime
>>> datetime.datetime.fromisoformat('2020-11-16T11:00:00+0000')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: Invalid isoformat string: '2020-11-16T11:00:00+0000'

This behavior is unexpected, as the ISO8601 standard allows omitting the colon in the string and defining the timezone as "<time>±hhmm
":

https://en.wikipedia.org/wiki/ISO_8601#Time_offsets_from_UTC

As a workaround, I normalized the timezone suffixes before parsing:

>>> if iso8601_string.endswith('+0000'):
>>>     return iso8601_string[:-len('+0000')] + '+00:00'
>>> if iso8601_string.endswith('+00'):
>>>     return iso8601_string[:-len('+00')] + '+00:00'
>>> if iso8601_string.endswith('-0000'):
>>>     return iso8601_string[:-len('-0000')] + '+00:00'
>>> if iso8601_string.endswith('-00'):
>>>     return iso8601_string[:-len('-00')] + '+00:00'

This only works for the UTC timezone. I would be nice to have a more general solution which can handle any timezone.

I tested this with CPython 3.8. `.fromisoformat()` was added in 3.7, so earlier versions should not be affected by this:

https://docs.python.org/3/library/datetime.html#datetime.date.fromisoformat

----------
components: Library (Lib)
messages: 381102
nosy: Bengt.Lüers
priority: normal
severity: normal
status: open
title: Missing colon in timezone suffix raises ValueError
type: behavior
versions: Python 3.8

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<https://bugs.python.org/issue42371>
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