監視對象變化的Python對象

Question

我想要一個Python對象，它可以監視自上次登錄後其他對象是否發生了更改，可能是通過存儲它們的哈希和比較來進行的。它應該是這樣的：

>>> library = Library() 
>>> library.is_changed(object1) 
False 
>>> object1.change_somehow() 
>>> library.is_changed(object1) 
True 
>>> library.is_changed(object1) 
False 

你知道這樣的事嗎？

Answer 1

這裏是你實現。請注意，您監視的對象必須是可哈希和可挑選的。還請注意，使用WeakKeyDictionary這意味着Monitor不會停止將被監視的對象刪除。

from weakref import WeakKeyDictionary 
from cPickle import dumps 

class Monitor(): 
    def __init__(self): 
     self.objects = WeakKeyDictionary() 
    def is_changed(self, obj): 
     current_pickle = dumps(obj, -1) 
     changed = False 
     if obj in self.objects: 
      changed = current_pickle != self.objects[obj] 
     self.objects[obj] = current_pickle 
     return changed 

class MyObject(): 
    def __init__(self): 
     self.i = 1 
    def change_somehow(self): 
     self.i += 1 

如果你測試它像這樣

object1 = MyObject() 
monitor = Monitor() 
print monitor.is_changed(object1) 
object1.change_somehow() 
print monitor.is_changed(object1) 
print monitor.is_changed(object1) 

它打印

False 
True 
False 

Answer 2

我還沒有聽說過這樣的事......但你可以很容易地寫出來。使用字典爲每個對象存儲名稱：散列對，然後使用pickle模塊保存字典。

Answer 3

聽起來像你在描述observer pattern。查看此處：

• http://rudd-o.com/projects/python-observable/
• Twisted observable
• http://radio.weblogs.com/0124960/2004/06/15.html#a30 - 包括解釋

Answer 4

我偷了尼克·克雷格 - 伍德的想法，並將其轉變爲混合級。對我來說，這是更容易使用：

from cPickle import dumps 

#base class for monitoring changes 
class ChangesMonitor: 
    _cm_last_dump = None 
    def is_changed(self): 
     prev_dump = self._cm_last_dump 
     self._cm_last_dump = None 
     cur_dump = dumps(self, -1) 
     self._cm_last_dump = cur_dump 
     return (prev_dump is not None) and (prev_dump != cur_dump) 

if __name__ == '__main__': 
    print 'Test Example' 

    #mix monitoring class with your regular class 
    class MyGreatObject(ChangesMonitor, object): 
     one_val = 5 
     second_val = 7 
     def some_changes(self): 
      self.second_val += 5 

    #and testing 
    my_obj = MyGreatObject() 
    print my_obj.is_changed() #False 
    print my_obj.is_changed() #False 
    my_obj.some_changes() 
    print my_obj.is_changed() #True 
    print my_obj.is_changed() #False 

Answer 5

這是基於Oduvan的答案，但作爲裝飾，而不是實現一個混合類：

from cPickle import dumps 

#decorator for monitoring changes 
def ChangesMonitor(cls): 

    def is_changed(self): 
     prev_dump = self._cm_last_dump 
     self._cm_last_dump = None 
     cur_dump = dumps(self, -1) 
     self._cm_last_dump = cur_dump 
     return (prev_dump is not None) and (prev_dump != cur_dump) 

    cls.is_changed = is_changed 
    cls._cm_last_dump = None 
    return cls 

print 'Test Example' 

#decorate your common class 
@ChangesMonitor 
class MyGreatObject(object): 
    one_val = 5 
    second_val = 7 
    def some_changes(self): 
     self.second_val += 5 

#and testing 
my_obj = MyGreatObject() 
print my_obj.is_changed() #False 
print my_obj.is_changed() #False 
my_obj.some_changes() 
print my_obj.is_changed() #True 
print my_obj.is_changed() #False 

注意@property能補def is_changed(self):行的前面，使得print my_obj.is_changed()將變爲print my_obj.is_changed。這可能會被認爲是更pythonic ...