A simplified deferred method

This is much like the twisted deferred, but is simplified down for use without twisted.

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1. class Deferred(object):  
2.     def __init__(self):  
3.         self._callbacks = []  
4.   
5.     def add_callback(self, callback):  
6.         if hasattr(self, 'result'):  
7.             callback(self.result)  
8.         else:  
9.             self._callbacks.append(callback)  
10.   
11.     def callback(self, result):  
12.         assert not hasattr(self, 'result')  
13.         for cb in self._callbacks:  
14.             cb(result)  
15.         self.result = result  
16.   
17.   
18. def defer(result):  
19.     d = Deferred()  
20.     d.result = result  
21.     return d  

class Deferred(object):
    def __init__(self):
        self._callbacks = []

    def add_callback(self, callback):
        if hasattr(self, 'result'):
            callback(self.result)
        else:
            self._callbacks.append(callback)

    def callback(self, result):
        assert not hasattr(self, 'result')
        for cb in self._callbacks:
            cb(result)
        self.result = result


def defer(result):
    d = Deferred()
    d.result = result
    return d