>>> s = pickle.dumps(timezone.utc)
>>> pickle.loads(s)
Traceback (most recent call last):
 ..
TypeError: ("Required argument 'offset' (pos 1) not found", <class 'datetime.timezone'>, ())

Python version is fixed in sandbox and committed in r82154.

Committed in r82184.  Leaving the issue open pending a more thorough review of pickling in datetime module.

The datetime module provides compact pickled representation for date, datetime, time and timedelta instances:

type: size
date: 34
datetime: 44
time: 36
timedelta: 37


On the other hand, current pickle size for timezone is 64 and the size of an aware datetime instance is 105 bytes.

Since stability is important for pickle format, the best format should be developed before the first release to include timezone class.

As part of this, we should ensure references to common timezones, like
UTC, only create references to a single instance rather than filling
memory with multiple instances.

One consequence of this is that shared instances should probably be immutable.

I am attaching a python prototype implementing interned UTC instance pickling.  The patch is against sandbox revision r82218 of datetime.py.

Note that the pickling protocol requires that an instance or factory function is defined at the module level.

The pickle size saving is substantial:


>>> len(dumps(datetime.now(timezone.utc)))
61
>>> len(dumps(datetime.now(timezone.min)))
163

but there is still room for improvement:

>>> len(dumps(datetime.now()))
44

I do feel, however, that further improvements will see diminishing returns.