问为什么键:值对不添加到字典中？

EN

if dup_agent_log.modify_stamp > merge_agent_log.modify_stamp:
    merge_agent_log.set_status_log(dup_agent_log.status, None, dup_agent_log.agents_id, dup_agent_log.source, dup_agent_log.status_type)
else:
    print merge_agent_log.data # {}
    now = str(datetime.datetime.now())
    merge_agent_log.data[now] = [{"status": dup_agent_log.status, "change_agent": dup_agent_log.change_agent, "source": dup_agent_log.source}]
    print "after", merge_agent_log.data # after {}

transaction.savepoint()

class AgentStatusLog(Base):
__tablename__ = "agent_status_log"
id = Column(
    Integer,
    Sequence("agent_status_log_id", optional=True),
    primary_key=True
)
status_id = Column(Integer, ForeignKey(StatusLookup.id))
_status = relationship(StatusLookup, uselist=False)
status = Column(Unicode(100), index=True)
previous_status = Column(Unicode(50), index=True)
effective_stamp = Column(DateTime, index=True)
modify_stamp = Column(DateTime, index=True)
agents_id = Column(Integer, ForeignKey(Agents.id))
agent = relationship(Agents, primaryjoin=Agents.id == agents_id, uselist=False)
_data = Column("data", Unicode(2048))
status_type = Column(Unicode(40), index=True)
change_agents_id = Column(Integer, ForeignKey(Agents.id))
change_agent = relationship(Agents, primaryjoin=Agents.id == change_agents_id, uselist=False)
source = Column(Unicode(100), index=True)


@property
def data(self):
    if not self._data:
        return {}
    return json.loads(self._data)

@data.setter
def data(self, value):
    self._data = json.dumps(value)

def set_data(self, field, value):
    data = self.data
    data[field] = value
    self.data = data

def get_data(self):
    if not self._data:
        return {}
    return json.loads(self._data)

def unset_data(self, field):
    data = self.get_data()
    if field in data:
        del data[field]
        self.data = data

@classmethod
def by_id(cls, id):
    return Session.query(cls).filter(cls.id == id).first()

@classmethod
def by_agents_id(cls, aid):
    return Session.query(cls).filter(cls.agents_id == aid).first()

@classmethod
def set_status_log(cls, status, change_agent=None, agent_id=None, source=None, status_type=None):
    if agent_id:
        sl = Session.query(cls).filter(cls.agents_id == agent_id).first()
        sl.modify_stamp = func.now()
        sl.source = source
        if sl.status:
            sl.previous_status = sl.status
            sl.data[str(datetime.datetime.now())] = [{"status": sl.status, "change_agent": change_agent, "source": source}]
        sl.status = status
        sl.change_agents_id = change_agent
        sl.status_type = status_type
        transaction.commit()