python - 运行时重载运算符

Question

是否可以在运行时重载运算符？我尝试了以下代码示例:

class A():
    pass
a = A()
a.__eq__ = lambda self, other: False
a == a # this should return False since the __eq__-method should be overloaded but it returns
       # True like object.__eq__ would
a.__eq__(a, a) # this returns False just as expected

为什么这段代码不起作用？是否有可能实现预期的行为？

Answer 1

魔术/双下划线方法是在类上查找的，而不是在实例上查找的。所以你需要重写类的方法，而不是实例。有两种方法可以做到这一点。

直接分配给类:

class A:
    pass

a = A()
A.__eq__ = lambda self, other: False
print(a == a)
print(a.__eq__(a)) # You're already passing in self by calling it as an instance method, so you only pass in the other one.

或者，如果您只有实例并且使用的是 3.x，则可以执行以下操作:

class A:
    pass

a = A()
type(a).__eq__ = lambda self, other: False
print(a == a)
print(a.__eq__(a))