[Sqlalchemy-tickets] Issue #4217: Can't pickle psycopg2.extensions objects (zzzeek/sqlalchemy)

[Marat S. <iss...@bi...>]

New issue 4217: Can't pickle psycopg2.extensions objects
https://bitbucket.org/zzzeek/sqlalchemy/issues/4217/cant-pickle-psycopg2extensions-objects

Marat Sharafutdinov:

I'm using Python 3.6.4, SQLAlchemy 1.2.5 (psycopg2 2.7.4 as adapter) and PostgreSQL 10.3.

Some exceptions are raised with `psycopg2.extensions` objects included. But I can't pickle these exceptions due to impossibility of pickling such objects.

Listing `test_pg.py`:
```
#!python

import pickle

import sqlalchemy as sa

url = 'postgresql://user:pass@host/test_db'
engine = sa.create_engine(url, echo=True)
connection = engine.connect()
metadata = sa.MetaData()
table = sa.Table('test_table', metadata,
    sa.Column('id', sa.Integer, primary_key=True),
    sa.Column('data', sa.LargeBinary),
)
metadata.create_all(engine)

try:
    engine.execute(table.insert(), {'id': 'invalid_integer', 'data': b'test'})
except Exception as exc:
    pickle.dumps(exc)
```
Output:
```
Traceback (most recent call last):
  File "test_pg.py", line 18, in <module>
    pickle.dumps(exc)
TypeError: can't pickle psycopg2.extensions.Binary objects
```

Refs to https://github.com/psycopg/psycopg2/issues/688.