Python的断言在属性设置

Question

是否有可能使属性断言当它（用于调试的目的）改变了吗？

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

编辑： 这是你在找什么？

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

添加一个布尔值来检查值时已设定：

编辑：但是你想要的属性，所以你需要创建一个：

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