问题描述
有没有什么神奇的方法可以重载赋值运算符,比如__assign__(self, new_value)
?
Is there a magic method that can overload the assignment operator, like __assign__(self, new_value)
?
我想禁止一个实例的重新绑定:
I'd like to forbid a re-bind for an instance:
class Protect():
def __assign__(self, value):
raise Exception("This is an ex-parrot")
var = Protect() # once assigned...
var = 1 # this should raise Exception()
有可能吗?是不是疯了?我应该吃药吗?
Is it possible? Is it insane? Should I be on medicine?
推荐答案
你描述的方式是绝对不可能的.给名字赋值是 Python 的一个基本特性,没有提供任何钩子来改变它的行为.
The way you describe it is absolutely not possible. Assignment to a name is a fundamental feature of Python and no hooks have been provided to change its behavior.
但是,可以根据需要控制对类实例中成员的分配,方法是覆盖 .__setattr__()
.
However, assignment to a member in a class instance can be controlled as you want, by overriding .__setattr__()
.
class MyClass(object):
def __init__(self, x):
self.x = x
self._locked = True
def __setattr__(self, name, value):
if self.__dict__.get("_locked", False) and name == "x":
raise AttributeError("MyClass does not allow assignment to .x member")
self.__dict__[name] = value
>>> m = MyClass(3)
>>> m.x
3
>>> m.x = 4
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 7, in __setattr__
AttributeError: MyClass does not allow assignment to .x member
请注意,有一个成员变量 _locked
控制是否允许赋值.您可以解锁它以更新值.
Note that there is a member variable, _locked
, that controls whether the assignment is permitted. You can unlock it to update the value.
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