support for psycopg2 on python 3

[Mike Bayer]

http://initd.org/psycopg/articles/2011/01/24/psycopg2-porting-python-3-report/

[Former user]

Psycopg 2.4 is out, with Python 3 support: http://initd.org/psycopg/articles/2011/02/27/psycopg-24-released/

Attempting to use it results in a nasty exception, though:

from sqlalchemy import schema, types
from sqlalchemy.engine import engine_from_config
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import scoped_session
from sqlalchemy.orm.session import sessionmaker

Base = declarative_base()

class User(Base):
    __tablename__ = 'users'

    id = schema.Column(types.Integer, autoincrement=True, primary_key=True)

engine = engine_from_config({'url': 'postgresql://user:password@host/database'}, '')
session = scoped_session(sessionmaker())
session.configure(bind=engine)

session.query(User).all()

Exception in 0.6.6:

Traceback (most recent call last):
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/pool.py", line 710, in do_get
    return self._pool.get(wait, self._timeout)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/queue.py", line 137, in get
    raise Empty
sqlalchemy.queue.Empty

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/orm/query.py", line 1580, in all
    return list(self)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/orm/query.py", line 1690, in __iter__
    return self._execute_and_instances(context)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/orm/query.py", line 1695, in _execute_and_instances
    mapper=self._mapper_zero_or_none())
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/orm/session.py", line 719, in execute
    return self._connection_for_bind(engine, close_with_result=True).execute(
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/orm/session.py", line 660, in _connection_for_bind
    return self.transaction._connection_for_bind(engine)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/orm/session.py", line 336, in _connection_for_bind
    conn = bind.contextual_connect()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 1831, in contextual_connect
    self.pool.connect(), 
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/pool.py", line 182, in connect
    return _ConnectionFairy(self).checkout()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/pool.py", line 369, in __init__
    rec = self._connection_record = pool.get()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/pool.py", line 213, in get
    return self.do_get()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/pool.py", line 732, in do_get
    con = self.create_connection()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/pool.py", line 147, in create_connection
    return _ConnectionRecord(self)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/pool.py", line 258, in __init__
    l.first_connect(self.connection, self)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/strategies.py", line 152, in first_connect
    dialect.initialize(c)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/dialects/postgresql/base.py", line 767, in initialize
    super(PGDialect, self).initialize(connection)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/default.py", line 151, in initialize
    self._get_server_version_info(connection)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/dialects/postgresql/base.py", line 918, in _get_server_version_info
    v = connection.execute("select version()").scalar()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 1191, in execute
    params)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 1287, in _execute_text
    return self.__execute_context(context)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 1312, in __execute_context
    r = context.get_result_proxy()._autoclose()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/dialects/postgresql/psycopg2.py", line 192, in get_result_proxy
    return base.ResultProxy(self)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 2266, in __init__
    self._init_metadata()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 2273, in _init_metadata
    self._metadata = ResultMetaData(self, metadata)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 2123, in __init__
    colname = colname.decode(dialect.description_encoding)
AttributeError: 'str' object has no attribute 'decode'

The 0.7b2 version also fails, with a slightly different outer exception:

Traceback (most recent call last):
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/pool.py", line 676, in _do_get
    return self._pool.get(wait, self._timeout)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/util/queue.py", line 137, in get
    raise Empty
sqlalchemy.util.queue.Empty

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/orm/query.py", line 1637, in all
    return list(self)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/orm/query.py", line 1747, in __iter__
    return self._execute_and_instances(context)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/orm/query.py", line 1753, in _execute_and_instances
    close_with_result=True).execute(querycontext.statement, self._params)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/orm/session.py", line 690, in connection
    close_with_result=close_with_result)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/orm/session.py", line 694, in _connection_for_bind
    return self.transaction._connection_for_bind(engine)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/orm/session.py", line 246, in _connection_for_bind
    conn = bind.contextual_connect()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 2062, in contextual_connect
    self.pool.connect(), 
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/pool.py", line 210, in connect
    return _ConnectionFairy(self).checkout()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/pool.py", line 374, in __init__
    rec = self._connection_record = pool._do_get()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/pool.py", line 698, in _do_get
    con = self._create_connection()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/pool.py", line 175, in _create_connection
    return _ConnectionRecord(self)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/pool.py", line 259, in __init__
    pool.dispatch.first_connect.exec_once(self.connection, self)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/event.py", line 214, in exec_once
    self(*args, **kw)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/event.py", line 223, in __call__
    fn(*args, **kw)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/strategies.py", line 162, in first_connect
    dialect.initialize(c)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/dialects/postgresql/base.py", line 766, in initialize
    super(PGDialect, self).initialize(connection)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/default.py", line 171, in initialize
    self._get_server_version_info(connection)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/dialects/postgresql/base.py", line 937, in _get_server_version_info
    v = connection.execute("select version()").scalar()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 1259, in execute
    params)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 1436, in _execute_text
    statement, parameters
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 1519, in _execute_context
    result = context.get_result_proxy()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/dialects/postgresql/psycopg2.py", line 198, in get_result_proxy
    return base.ResultProxy(self)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 2420, in __init__
    self._init_metadata()
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 2427, in _init_metadata
    self._metadata = ResultMetaData(self, metadata)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/engine/base.py", line 2283, in __init__
    colname = dialect._description_decoder(colname)
  File "/usr/lib64/python3.1/site-packages/sqlalchemy/processors.py", line 69, in process
    return decoder(value, errors)[0](0)
  File "/usr/lib64/python3.1/encodings/utf_8.py", line 16, in decode
    return codecs.utf_8_decode(input, errors, True)
TypeError: must be bytes or buffer, not str

[Mike Bayer]

this was implemented as of 0.7b4.

[Mike Bayer]

Removing milestone: 0.7.0 (automated comment)