https://docs.python.org/3/library/datetime.html#datetime-objects
gives in an example two classes named GMT1 and GMT2 subclassing tzinfo, defined with dst(…) methods returning one hour timedelta for summer periods. This is in conflict with naming, as GMT timezone is not defined with any daylight saving time, so any timezone offsetted from it shouldn't be as well. I would suggest renaming them to something like BrusselsTZ and HelsinkiTZ (with a comment that this is simplified implementation, that doesn't account for exact hour when dst switch is made, and maybe mentioning pytz) and tzname(…) to return ('CET', 'CEST')[bool(self.dst(dt))] and ('EET', 'EEST')[bool(self.dst(dt))] accordingly.

Also https://docs.python.org/3/library/datetime.html#time-objects
has an example with GMT1 class, though this time dst(…) unconditionally returns offset 0 properly, tzname(…) gives 'Europe/Prague' – region that uses dst. IMHO returning any of: "CET", "GMT+1", "Africa/Tunis" would be better here.

New changeset f0b5ae4567637b24035ecda93a3240efc96b6dd9 by Victor Stinner (Mario Corchero) in branch 'master':
bpo-30699: Improve example on datetime tzinfo instances (GH-4290)
https://github.com/python/cpython/commit/f0b5ae4567637b24035ecda93a3240efc96b6dd9

New changeset 12c178799a23b47c5f8ebc072cbdf09a370649ae by Miss Islington (bot) in branch '3.7':
bpo-30699: Improve example on datetime tzinfo instances (GH-4290)
https://github.com/python/cpython/commit/12c178799a23b47c5f8ebc072cbdf09a370649ae

Thanks Mario Corchero for the doc enhancement, and Paul for the review!

Python 2.7 is not affected: datetime has no timeinfo class.