[PonyORM-list] offset aware datetimes => bad idea with pony orm

[stephane martin]

hello,

just a short note: ponyorm doesnt feel very comfortable with tz-aware
python datetimes in schemas. That's... well... not a surprise, i shoud
have expected it if i had thought about it 5 minutes.

I have something like:

"""
class Message(db.Entity):
    id = PrimaryKey(int, auto=True)
    subject = Optional(unicode)
    client_hostname = Optional(unicode)
    helo_hostname = Optional(unicode)
    message_id = Optional(unicode)
    importance = Optional(unicode)
    priority = Optional(unicode)
    sensitivity = Optional(unicode)
    size = Optional(int)
    content_type = Optional(unicode)
    creator_date = Optional(datetime.datetime)
"""

I feed it with a tz-aware creator_date. Creation succeeds, but
afterwards updating the object fails with:

"""
  File "<auto generated wrapper of __new__() function>", line 2, in __new__
  File "/Users/steph/dev/manager_env/lib/python2.7/site-packages/pony/utils.py",
line 64, in cut_traceback
    return func(*args, **kwargs)
  File "/Users/steph/dev/manager_env/lib/python2.7/site-packages/pony/orm/core.py",
line 3468, in __new__
    if attr.reverse: attr.update_reverse(obj, None, val, undo_funcs)
  File "/Users/steph/dev/manager_env/lib/python2.7/site-packages/pony/orm/core.py",
line 1484, in update_reverse
    if new_val is not None: reverse.__set__(new_val, obj, undo_funcs)
  File "<auto generated wrapper of __set__() function>", line 2, in __set__
  File "/Users/steph/dev/manager_env/lib/python2.7/site-packages/pony/utils.py",
line 64, in cut_traceback
    return func(*args, **kwargs)
  File "/Users/steph/dev/manager_env/lib/python2.7/site-packages/pony/orm/core.py",
line 1370, in __set__
    old_val = attr.load(obj)
  File "/Users/steph/dev/manager_env/lib/python2.7/site-packages/pony/orm/core.py",
line 1332, in load
    else: obj._load_()
  File "/Users/steph/dev/manager_env/lib/python2.7/site-packages/pony/orm/core.py",
line 3541, in _load_
    objects = entity._fetch_objects(cursor, attr_offsets)
  File "/Users/steph/dev/manager_env/lib/python2.7/site-packages/pony/orm/core.py",
line 3126, in _fetch_objects
    obj._db_set_(avdict)
  File "/Users/steph/dev/manager_env/lib/python2.7/site-packages/pony/orm/core.py",
line 3568, in _db_set_
    elif old_dbval == new_dbval:
TypeError: can't compare offset-naive and offset-aware datetimes
"""

IIRC sqlalchemy suffers from that too. Not sure there is an elegant
solution (obviously the pony doesnt know anything about the tz library
im using - pytz). So i probably have to stick to naive datetimes.

Cheers,
Stephane