gistfile1.py

class Proposal:
    def _get_state_log(self, memo={}):
        print memo
        # return cached log if it appears to be correct
        if 'log' in memo:
            if self.status == memo['log'].state:
                print 'returning cached value'
                return memo['log']

        print 'executing query'
        log = StateLog.objects.for_(self).order_by('-id')[0]
        memo['log'] = log
        return log
        
...


In [3]: proposal._get_state_log()
{}
executing query
Out[3]: <StateLog: StateLog object>

In [4]: proposal._get_state_log().state
{'log': <StateLog: StateLog object>}
executing query
Out[4]: u'submitted'

In [5]: proposal.approve()

In [6]: proposal._get_state_log()
{'log': <StateLog: StateLog object>}
executing query
Out[6]: <StateLog: StateLog object>

In [7]: proposal._get_state_log()
{'log': <StateLog: StateLog object>}
returning cached value
Out[7]: <StateLog: StateLog object>

In [8]: proposal._get_state_log()
{'log': <StateLog: StateLog object>}
returning cached value
Out[8]: <StateLog: StateLog object>