Many parts of the code raise None exception rather than original exception, that can not find the real error。

[Former user]

Many parts of the code raise None exception rather than original exception, that can not find the real error。

For example: SQLAlchemy-0.7.1/sqlalchemy/orm/session.py, in line 1561, in _flush

Because i use eventlet.db_pool without charset option, I got TypeError: exceptions must be old-style classes or derived from BaseException, not NoneType, but actually encoding errors。

[Mike Bayer]

Need detailed information about the specific issue, description is too vague (note the guidelines for posting bugs at http://www.sqlalchemy.org/participate.html#bugs request that a full, succinct, reproducing test case for the bug is attached).

Line 1561 of _session.py does not handle user input or by itself raise any exception:

flush_context = UOWTransaction(self)

SQLAlchemy exceptions derive from SQLAlchemyError, which in turn derives from Python's base Exception class (line 17, exc.py):

class SQLAlchemyError(Exception):
    """Generic error class."""

They don't extend from NoneType, which is not even possible in Python.

Per Python's own documentation, inheriting from Exception is the correct approach. See #2160. Citing http://docs.python.org/library/exceptions.html:

The built-in exception classes can be sub-classed to define new exceptions; programmers are encouraged to at least **derive new exceptions from the Exception class and not BaseException**. More information on defining exceptions is available in the Python Tutorial under User-defined Exceptions.

And directly below that:

exception BaseException

The base class for all built-in exceptions. **It is not meant to be directly inherited by user-defined classes (for that, use Exception)**.

I'm not familiar with eventlet.db_pool, though SQLAlchemy does not currently have supported integration paths with asynchronous systems. Certainly if it requires that exceptions are implemented as old style classes and not extending Exception, that's a bug in eventlet, not SQLAlchemy.

[Mike Bayer]

SQLA 0.7.1, line 1561:

      except:
            transaction.rollback(_capture_exception=True)
            raise

This is a standard Python re-raise (documented at http://docs.python.org/tutorial/errors.html#handling-exceptions). The exception information retrieved from the except: is maintained.

[Mike Bayer]

OK it seems this is an issue on the eventlet side, doing a worksforme here.