I have the following database schema

class posts(Base):
    __tablename__ = 'xposts'
    id = Column(Integer, primary_key=True) 



class Comments(Base):  
    __tablename__ = 'comments'
    id = Column(Integer, primary_key=True) 
    comment_parent_id=Column(Integer,unique=True)  
    #comment_id fetches comment of a comment ie the comment_parent_id
    comment_id=Column(Integer,default=None)
    comment_text=Column(String(200))

Values in database are

1   12  NULL    Hello First comment
2   NULL    12  First Sub comment

I want to fetch all Comments and sub comments of a post using sqlalchemy and have this so far

qry=session.query(Comments).filter(Comments.comment_parent_id!=None)
print qry.count()

Is there a way i can fetch the all the subcomments of a comment in a query i have tried outerjoin on the same table(comments) and it seemed stupid and it failed.