"Invalid column expression" error message could be vastly improved

When query(...) is run, it appears that if it cannot figure out what to do with its argument, then it prints the very confusing error message:

sqlalchemy.exc.InvalidRequestError: Invalid column expression ...

What I really needed it to say, in my case, is that "You have handed me a plain class that has not been properly hooked up to SQLAlchemy through an ORM mapper, so I don't know how to query it." It took me quite a bit of work to get from the error message to the fact that I had forgotten to have Pylons call init_model(). :-)

Of course, since there are lots of possible things that get handed to query(), and classes are only one of them, the message can't just handle my case; but the fact that it chooses instead to address another case — the possibility that someone is asking for a particular column? — just generates confusion.

If the message needs to remain short, it could be re-worded to something like:

sqlalchemy.exc.InvalidRequestError: query() has been called
with an object that does not identify a database table or query

Better yet (but maybe SQLAlchemy doesn't like long messages?) would be:

sqlalchemy.exc.InvalidRequestError: query() needs to be supplied
with a table name, column name, or a table or column object mapped
with the SQLAlchemy ORM; instead, it has been called with: <...object...>

Anyway, if the error message could stop talking about columns when the problem was that I hadn't made my web framework call my ORM mapper() command, it would take less time to debug it.

Here's some test code that causes the error:

import sqlalchemy
from sqlalchemy.orm import sessionmaker

engine = sqlalchemy.create_engine('sqlite:///:memory:')
Session = sessionmaker(bind=engine)

class Test(object):
    pass

Session().query(Test)

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