gistfile1.txt

from sqlalchemy.orm import Query
from sqlalchemy.orm.exc import MultipleResultsFound

class MyQuery(Query):
    def get_byusername(self, username):
        ret = list(self.filter(username=username))
        r_len = let(ret)
        
        if r_len == 1:
            return ret[0]
        elif r_len == 0:
            return None
        else:
            raise MultipleResultsFound('Multiple rows were found for get_username({})'.format(username))
            
session = Session(query_cls=MyQuery)
session.query(User).get_byusername(some_username)