AttributeError when removing an event in SQLAlchemy 1.2.3

[sqlalchemy-bot]

Migrated issue, originally created by href (@href)

When removing a registered Event on the Engine class in SQLAlchemy 1.2.3 I get an AttributeError.

Code:

from sqlalchemy import event
from sqlalchemy.engine import Engine

@event.listens_for(Engine, 'after_cursor_execute')
def after_cursor_execute(*args, **kwargs):
    pass

event.remove(Engine, 'after_cursor_execute', after_cursor_execute)

Setup:

python3.6 -m venv test
cd test
bin/pip install sqlalchemy
bin/python test.py

Stacktrace:

Traceback (most recent call last):
  File "test.py", line 8, in <module>
    event.remove(Engine, 'after_cursor_execute', after_cursor_execute)
  File "/private/tmp/test/lib/python3.6/site-packages/sqlalchemy/event/api.py", line 178, in remove
    _event_key(target, identifier, fn).remove()
  File "/private/tmp/test/lib/python3.6/site-packages/sqlalchemy/event/registry.py", line 220, in remove
    collection.remove(self.with_wrapper(listener_fn))
  File "/private/tmp/test/lib/python3.6/site-packages/sqlalchemy/event/attr.py", line 167, in remove
    self._clslevel[cls].remove(event_key._listen_fn)
AttributeError: '_empty_collection' object has no attribute 'remove'

Only SQLAlchemy 1.2.3 seems to be affected. 1.2.2 works. I'm using Python 3.6 on MacOS High Sierra. Additionally I use Psycopg2.7.4 and Postgres 10.1, though from what I can tell that is not relevant here since I can reproduce the error in a clean virtualenv.

[sqlalchemy-bot]

Changes by href (@href):

• edited description

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

I know what this is and you should be able to use 1.2.2. I am very much hoping to fix and release 1.2.4 today however other issues seem like they are going to make this more challenging to achieve.

[sqlalchemy-bot]

Changes by Michael Bayer (@zzzeek):

• added labels: blocker

[sqlalchemy-bot]

Changes by Michael Bayer (@zzzeek):

• set milestone to "1.2.x"

[sqlalchemy-bot]

href (@href) wrote:

I'm absolutely okay using 1.2.2 and have in fact already added sqlalchemy!=1.2.3 to my requirements. No pressure from my side ;)

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

Implement remove() for _empty_collection

Fixed regression caused in 1.2.3 due to fix from 🎫4181 where
the changes to the event system involving :class:.Engine and
:class:.OptionEngine did not accommodate for event removals, which
would raise an AttributeError when invoked at the class
level.

Change-Id: I1c9083829d74dd710716d28b0eaca4fa15e86313
Fixes: #4190

→ 1393eac

[sqlalchemy-bot]

Changes by Michael Bayer (@zzzeek):

• changed status to closed

[sqlalchemy-bot]

href (@href) wrote:

Thank you!