import time class TimeDict(dict):
    def __init__(self,*args,**kwargs):
        dict.__init__(self,*args,**kwargs)
        self.orderedKeys = self.keys()
    def __setitem__(self,key,value):
        dict.__setitem__(self,key,(time.time(),value))
        if key in self.orderedKeys:
            self.orderedKeys.remove(key)
        self.orderedKeys.append(key)
    def __delitem__(self,key):
        dict.__delitem__(self,key)
        self.orderedKeys.remove(key)
    def __getitem__(self,key):
        return dict.__getitem__(self,key)[1]
    def olderThan(self,timeout):
        t = time.time()-timeout
        result = {}
        for key in self.orderedKeys:
            timestamp,value = dict.__getitem__(self,key)
            if timestamp < t:
                result[key]=value
            else:
                break
        return result

Sample Usage: 
>>> from timeDict import TimeDict
>>> a = TimeDict()  
>>> a['foo'] = 'bar'
>>> a['bar'] = 'baz'
>>> a.olderThan(10)  # key/value pairs older than 10 seconds
{'foo': 'bar'}
>>> a.olderThan(10)
{'foo': 'bar', 'bar': 'baz'}