Python的斷言在屬性設置

Question

是否有可能使屬性斷言當它（用於調試的目的）改變了嗎？

class MyClass(object): 
    def set_my_property(self, value): 
     self.my_property = value 
     # TODO: mark my_property so that if it gets set again, an assert 
     # is triggered 

c = MyClass() 
c.set_my_property(4) 

# any of these lines would cause an assertion 
c.set_my_property(8) 
c.my_property = 123 

Answer 1

編輯： 這是你在找什麼？

class MyClass(object): 
    def __init__(self): 
     self.trigger = False 
     self._my_property = 0 

    def set_my_property(self, value): 
     if self.trigger: 
      raise Exception("WHOOPS!") 
     self._my_property = value 
     # TODO: mark my_property so that if it gets set again, an assert 
     # is triggered 
     self.trigger = True 

    def get_my_property(self): 
     return self._my_property 

    my_property = property(get_my_property, set_my_property, None) 

c = MyClass() 
c.set_my_property(4) 

# any of these lines would cause an assertion 
c.set_my_property(8) 
c.my_property = 123 

Answer 2

class Foo: 
    def __init__(self): 
     self._bar = None 

    @property 
    def bar(self): return self._bar 

    @bar.setter: 
    def bar(self, value): 
     assert value != some_constant # your assert condition 
     self._bar = value 

    @bar.deleter: 
    def bar(self, value): 
     assert value != some_constant # your assert condition 
     self._bar = None 

Answer 3

添加一個布爾值來檢查值時已設定：

編輯：但是你想要的屬性，所以你需要創建一個：

class MyClass(object): 
    def __init__(self): 
     self.my_property_set = False 
     self._my_property = None 

    def set_my_property(self, value): 
     self._my_property = value 
     assert not self.my_property_set,"my_property already set" 
     self.my_property_set = True 

    def get_my_property(self): 
     return self._my_property 

    my_property = property(get_my_property, set_my_property, None) 

c = MyClass() 
c.set_my_property(4) 

# any of these lines would cause an assertion 
c.set_my_property(8) 
c.my_property = 123