监视对象更改的python对象

下面是一个实现。请注意,您监视的对象必须是可哈希和可拾取的。同时注意使用 WeakKeyDictionary 这意味着 Monitor 不会阻止被监视对象被删除。

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

如果你像这样测试它

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

资讯科技印刷

False
True
False

听起来你在描述 observer pattern . 在这里检查:

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

我从尼克·克雷格·伍德那里偷了这个主意,把它改成了混合班。对我来说,这更容易使用:

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

我没听说过这样的事…但你可以很容易地写出来。使用字典存储每个对象的name:hash对,然后使用 pickle 用于保存字典的模块。

这是基于oduvan的答案,但实现为一个修饰器而不是类中的混合:

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 可以添加到 def is_changed(self): 这样行 print my_obj.is_changed() 将成为 print my_obj.is_changed . 这可能被认为是更多的蟒蛇…