pypi / python-dateutil

python-dateutil

What changed in python-dateutil 3, from its official release notes, upgrade guides and advisories. Sources checked 2026-10-22.

6 breaking1 deprecations2 new APIs and options2 behavior and defaults5 fixes and other

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python-dateutil 316 changes

The mutable search-path list has been removed; use dateutil.tz.TZPATH and dateutil.tz.reset_tzpath instead.
3.0.0release notes
The function no longer does anything and raises RebuildDeprecationWarning as an error by default.
3.0.0release notes
Passing a relative key that refers to a file outside every directory on TZPATH is deprecated and raises DeprecatedTzKeyWarning as an error by default.
3.0.0release notes
The minimum supported version is now 1.6, fixing No module named 'six.moves' errors with older versions.
3.0.0release notes
The package no longer bundles the IANA database; data comes from the system or the installed tzdata package.
3.0.0release notes
For times in a gap, fold=0 uses the pre-transition offset and fold=1 uses the post-transition offset, following PEP 495.
3.0.0release notes

The module is deprecated and now wraps tzdata; users are encouraged to migrate to dateutil.tz.gettz or the standard library's zoneinfo.
3.0.0release notes

Allows runtime configuration of the IANA time zone data search path.
3.0.0release notes
Provides the time zone data search path, which can be configured at runtime.
3.0.0release notes

Cached instances can now be pickled and deep-copied; cache settings are preserved and cached results regenerated on demand.
3.0.0release notes
Cached instances can now be pickled and deep-copied; cache settings are preserved and cached results regenerated on demand.
3.0.0release notes

Comparing against an unsupported type such as None now returns True instead of raising TypeError.
3.0.0release notes
Experimental X- parameters in an RRULE line are now ignored instead of raising ValueError, as RFC 5545 permits.
3.0.0release notes
The rewrite supports Version 2 and Version 3 tzfile binaries, resolving issues with timestamps beyond 2038 and slim format binaries.
3.0.0release notes
Fixed-offset zones now return their offset, DST offset, and abbreviation when utcoffset, dst, and tzname are called with None, making attached datetime.time objects aware.
3.0.0release notes
dst() is inferred from standard time on both sides of each DST period and for each transition, fixing several double, half-hour, and changing-standard-offset cases.
3.0.0release notes