[Sqlalchemy-tickets] Issue #3302: reset isolation level fails on invalided connection (zzzeek/sqlalchemy)

[Mike B. <iss...@bi...>]

New issue 3302: reset isolation level fails on invalided connection
https://bitbucket.org/zzzeek/sqlalchemy/issue/3302/reset-isolation-level-fails-on-invalided

Mike Bayer:


```
#!python

>>> from sqlalchemy import create_engine
>>> e = create_engine("sqlite://")  
>>> c1 = e.connect()
>>> c2 = c1.execution_options(isolation_level='SERIALIZABLE')
>>> c2.invalidate()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/classic/dev/sqlalchemy/lib/sqlalchemy/engine/base.py", line 482, in invalidate
    self._root.__connection.invalidate(exception)
  File "/Users/classic/dev/sqlalchemy/lib/sqlalchemy/pool.py", line 759, in invalidate
    self._checkin()
  File "/Users/classic/dev/sqlalchemy/lib/sqlalchemy/pool.py", line 682, in _checkin
    self._pool, None, self._echo, fairy=self)
  File "/Users/classic/dev/sqlalchemy/lib/sqlalchemy/pool.py", line 580, in _finalize_fairy
    connection_record.checkin()
  File "/Users/classic/dev/sqlalchemy/lib/sqlalchemy/pool.py", line 466, in checkin
    finalizer(connection)
  File "/Users/classic/dev/sqlalchemy/lib/sqlalchemy/engine/default.py", line 454, in reset_isolation_level
    self.set_isolation_level(dbapi_conn, self.default_isolation_level)
  File "/Users/classic/dev/sqlalchemy/lib/sqlalchemy/dialects/sqlite/base.py", line 868, in set_isolation_level
    cursor = connection.cursor()
AttributeError: 'NoneType' object has no attribute 'cursor'
>>> 

```