JSONEncoder

A flat implementation
You could use something like this:

from sqlalchemy.ext.declarative import DeclarativeMeta
class AlchemyEncoder(json.JSONEncoder):
def default(self, obj):
    if isinstance(obj.__class__, DeclarativeMeta):
        # an SQLAlchemy class
        fields = {}
        for field in [x for x in dir(obj) if not x.startswith('_') and x != 'metadata']:
            data = obj.__getattribute__(field)
            try:
                json.dumps(data) # this will fail on non-encodable values, like other classes
                fields[field] = data
            except TypeError:
                fields[field] = None
        # a json-encodable dict
        return fields

    return json.JSONEncoder.default(self, obj)
and then convert to JSON using:

c = YourAlchemyClass()
print json.dumps(c, cls=AlchemyEncoder)