python - 装饰器中的无限递归(类似乎是从自身继承的)

Question

我在装饰类中看到无限递归:

def my_decorator():
    def class_decorator(cls):
        class NewClass(cls):
            @classmethod
            def func(cls):
                print "decorator"
                super(NewClass, cls).func()

        return NewClass
    return class_decorator

class B(object):
    @classmethod
    def func(cls):
        print "Root"

@my_decorator()
class A(B):
    @classmethod
    def func(cls):
        print "func"
        super(A, cls).func()


x = A()    
x.func()

输出:

decorator
func
func
func
func
... <lots of 'func'> ...
lots of these:
  File "test.py", line 22, in func
    super(A, cls).func()
  File "test.py", line 22, in func
    super(A, cls).func()
  File "test.py", line 22, in func
    super(A, cls).func()
RuntimeError: maximum recursion depth exceeded while calling a Python object

没有装饰器，它返回:

func
Root

...正如预期的那样。

这是怎么回事？

Answer 1

在你装饰了原来的A之后，相当于:

A = my_decorator()(A)

名称A指的是新创建的NewClass，它也继承了原来的A，不是原始的 A。因此 super(A, cls).func 总是解析为 super(NewClass, cls).func，即 A.func。

展开装饰器并将结果分配给一个不同的名称，您会得到正确的行为:

X = my_decorator()(A)
x = X()
x.func()

给出:

decorator
func
Root