dateutil/dateutil

Parser UTC offset logic is inverted

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#70 opened on Mar 31, 2015

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enhancementhelp wantedmedium-difficultyparsertime zones

Description

my python-dateutil version: 2.4.1

i am in the time zone: CST(UTC+8)

when i use dateutil, it return different with other tools

pyhton-dateutil:

In [21]: parse("2015-03-31 00:01 UTC").astimezone(cst)
Out[21]: datetime.datetime(2015, 3, 31, 8, 1, tzinfo=tzlocal())

In [22]: parse("2015-03-31 00:01 UTC+1").astimezone(cst)
Out[22]: datetime.datetime(2015, 3, 31, 9, 1, tzinfo=tzlocal())

In [23]: parse("2015-03-31 00:01 UTC-1").astimezone(cst)
Out[23]: datetime.datetime(2015, 3, 31, 7, 1, tzinfo=tzlocal())

linux date command:

yu at debian in ~ 
(! 4076)-> date -d "2015-03-31 00:01 UTC"
Tue Mar 31 08:01:00 CST 2015
yu at debian in ~ 
(! 4076)-> date -d "2015-03-31 00:01 UTC+1"
Tue Mar 31 07:01:00 CST 2015
yu at debian in ~ 
(! 4077)-> date -d "2015-03-31 00:01 UTC-1"
Tue Mar 31 09:01:00 CST 2015

Contributor guide

Tech stack
python
Domain
backend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Basic understanding of Python datetime and timezones
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Investigate the parser logic in dateutil's parser.py. The bug is that the sign of the UTC offset is inverted when parsing strings like 'UTC+1' and 'UTC 1'. Compare with Linux date command behavior. The fix involves inverting the sign when converting the offset to a timezone object. Check the relevant code that handles the UTC offset token.