如何确定SQLAlchemy会话是否需要comit

Question

如何确定SQLAlchemy会话是否需要提交？以下是示例代码：

    #!/usr/bin/env python
    import sys
    import os
    from sqlalchemy import create_engine
    from sqlalchemy.orm import sessionmaker
    from sqlalchemy.ext.declarative import declarative_base
    from sqlalchemy import Column, Integer, String, ForeignKey
    from sqlalchemy.orm import relation, validates

    DeclBase = declarative_base()
    class Parent(DeclBase):
        __tablename__ = 'parent'
        id = Column('id', Integer, primary_key=True)
        name = Column('name', String)
        children = relation('Child', back_populates='parent')

        def __repr__(self):
            return "<Parent(id='%d', name='%s')>" % (self.id, self.name)
        def __init__ (self, id, name=''):
            self.id = id
            self.name = name

    class Child(DeclBase):
        __tablename__ = 'child'
        id = Column('id', Integer, primary_key=True)
        name = Column('name', String)
        parent_id = Column('parent', Integer, ForeignKey('parent.id'))
        parent = relation('Parent', back_populates='children')

        def __repr__(self):
            return "<Child(id='%d', name='%s')>" % (self.id, self.name)
        def __init__ (self, id, parent, name=''):
            self.id = id
            self.name = name
            self.parent_id = parent

    ## Main()

    dbengine = create_engine('postgresql://{}:{}@{}:{}/{}'.format(
        'swms-dba', 'swms-dba', 'localhost', 5432, 'swmsdb'),                                                 
        client_encoding='utf8')
    dbsession = sessionmaker(bind=dbengine)()
    p1 = Parent(1,'Parent')
    dbsession.add(p1)
    c1 = Child(1,1,'Child#1')
    dbsession.add(c1)
    c2 = Child(2,1,'Child#2')
    dbsession.add(c2)

    print('Before:', dbsession.dirty, dbsession.new, dbsession.deleted)

    query = dbsession.query(Parent).filter(Parent.id==1)
    if query.count() == 1:
        parent=query.one()
        print(parent)
        for child in parent.children:
            print(child)

    print('After:', dbsession.dirty, dbsession.new, dbsession.deleted)
    dbsession.close()

    ## End

产生的输出是：

    >test.py
    Before: IdentitySet([]) IdentitySet([<Parent(id='1', name='Parent')>,
             <Child(id='1', name='Child#1')>,
             <Child(id='2', name='Child#2')>]) IdentitySet([])
    <Parent(id='1', name='Parent')>
    <Child(id='1', name='Child#1')>
    <Child(id='2', name='Child#2')>
    After: IdentitySet([]) IdentitySet([]) IdentitySet([])

如果我在调用sessionmaker（）时将autoflush设置为False，则IdentitySets在第二次打印时不会变空。但是，query（）并没有任何实例:(看起来像autoflush设置为True，query（）触发刷新，清空IdentitySet