SQLAlchemy - Mapping ResultProxy to mapped classes without a session
session.query(SomeClass)

engine = create_engine('sqlite:///:memory:')
meta = MetaData()
meta.bind = engine
table = Table('table, meta,
    Column('id', Integer, primary_key=True),
    Column('field1', String(16), nullable=False),
    Column('field2', String(60)),
    Column('field3', String(20), nullable=False)
)

class Table(object)
    pass

meta.create_all(checkfirst=True)
for i in range(10):
    user.insert({'field1': 'field1'+i,'field2': 'field2'+i*2,'field3': 'field3'+i*4})
mapper(Table, table)
query = Query((Table,))
query.instances(engine.text("SELECT * FROM table").execute())

Traceback (most recent call last):
    File "sqlalchemy/orm/mapper.py", line 2507, in _instance_processor
        session_identity_map = context.session.identity_map
    AttributeError: 'NoneType' object has no attribute 'identity_map'