Version 2.8.1 (2019-11-03)

Data updates

Fixed a race condition in the tzoffset and tzstr "strong"
caches on Python 2.7. Reported by @kainjow (gh issue #901).
Parsing errors will now raise ParserError, a subclass of
ValueError, which has a nicer string representation. Patch by
@gfyoung (gh pr #881).
parser.parse will now raise TypeError when tzinfos is passed a
type that cannot be interpreted as a time zone. Prior to this
change, it would raise an UnboundLocalError instead. Patch by
@jbrockmendel (gh pr #891).
Changed error message raised when when passing a bytes object as
the time zone name to gettz in Python 3. Reported and fixed by
@labrys () (gh issue #927, gh pr #935).
Changed compatibility logic to support a potential Python 4.0
release. Patch by Hugo van Kemenade (gh pr #950).
Updated many modules to use tz.UTC in favor of tz.tzutc()
internally, to avoid an unnecessary function call. (gh pr #910).
Fixed issue where dateutil.tz was using a backported version of
contextlib.nullcontext even in Python 3.7 due to a malformed
import statement. (gh pr #963).

Switched from using assertWarns to using pytest.warns in the test
suite. (gh pr #969).
Fix typo in setup.cfg causing PendingDeprecationWarning to not be
explicitly specified as an error in the warnings filter. (gh pr
#966)
Fixed issue where test_tzlocal_offset_equal would fail in certain
environments (such as FreeBSD) due to an invalid assumption about
what time zone names are provided. Reported and fixed by Kubilay
Kocak (gh issue #918, pr #928).
Fixed a minor bug in test_isoparser related to bytes/str
handling. Fixed by @fhuang5 (gh issue #776, gh pr #879).
Explicitly listed all markers used in the pytest configuration. (gh
pr #915)
Extensive improvements to the parser test suite, including the
adoption of pytest-style tests and the addition of parametrization
of several test cases. Patches by @jbrockmendel (gh prs #735,
#890, #892, #894).
Added tests for tzinfos input types. Patch by @jbrockmendel (gh pr
#891).
Fixed failure of test suite when changing the TZ variable is
forbidden. Patch by @shadchin (gh pr #893).
Pinned all test dependencies on Python 3.3. (gh prs #934, #962)

Fixed many misspellings, typos and styling errors in the comments
and documentation. Patch by Hugo van Kemenade (gh pr #952).

Added Python 3.8 to the trove classifiers. (gh pr #970)
Moved as many keys from setup.py to setup.cfg as possible. Fixed
by @FakeNameSE, @aquinlan82, @jachen20, and @gurgenz221 (gh
issue #871, gh pr #880).
Reorganized parser methods by functionality. Patch by
@jbrockmendel (gh pr #882).
Switched release.py over to using pep517.build for creating
releases, rather than direct invocations of setup.py. Fixed by
@smeng10 (gh issue #869, gh pr #875).
Added a "build" environment into the tox configuration, to handle
dependency management when making releases. Fixed by @smeng10 (gh
issue #870,r gh pr #876).
GH #916, GH #971