[Sqlalchemy-tickets] Issue #3974: Inconsistent session state after raising exception in after_commit event (zzzeek/sqlalchemy)

[Oleg L. <iss...@bi...>]

New issue 3974: Inconsistent session state after raising exception in after_commit event
https://bitbucket.org/zzzeek/sqlalchemy/issues/3974/inconsistent-session-state-after-raising

Oleg Lomaka:

If you raise an exception in after_commit event handler, then session.is_active is False, but if you try to call session.begin(), you will get an error: "This session is in 'committed' state; no further SQL can be emitted within this transaction."

session.begin() will work only after manually calling session.close(). I am not sure is it ok to call close in this case. And not sure you consider this as actually a bug, but apparently the session is in some inconsistent state after raising exception in after_commit event handler.

```
#!python

@event.listens_for(session, 'after_commit')
def handler(session):
    raise Exception

try:
    with session.begin():
        pass
except Exception as e:
    pass

session.begin() # raises "This session is in 'committed' state; no further SQL can be emitted within this transaction."
```