python - 如何在派生的python类上操作装饰器？

Question

我想使用装饰器对派生类做一些事情(例如注册类或其他东西)。这是我的代码:

from functools import wraps

class Basic(object):
    def __init__(self):
        print "Basic::init"

def myDeco(name):
    # define the decorator function that acts on the actual class definition
    def __decorator(myclass):

        # do something here with the information
        print name, myclass

        # do the wrapping of the class 
        @wraps(myclass)
        def __wrapper(*args, **kwargs):
            return myclass( *args, **kwargs)

        # return the actual wrapper here
        return __wrapper

    # return the decorator to act on the class definition
    return __decorator

@myDeco("test")
class Derived(Basic):
    def __init__(self):
        super(Derived, self).__init__()
        print "Derived::init"


instance = Derived()

出现以下错误:

TypeError: must be type, not function

当 Derived 中的 super 方法被调用时。我假设变量 Derived 不再是 type，而是函数 __decorator。

我需要如何更 retrofit 饰器(并且仅更 retrofit 饰器)才能解决此问题？

Answer 1

您正在用函数替换装饰类，因此类定义失败。

具体来说，super(Derived, self).__init__() 现在将一个函数 传递给 super():

>>> super(Derived, object())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: must be type, not function
>>> type(Derived)
<type 'function'>

类装饰器通常改变类，添加、删除或改变它的属性，然后再次返回类对象。

您应该不将Derived 替换为新类，因为您的Derived.__init__() 通过名称引用自身。用另一个类替换该名称将导致痛苦(例如无限递归)。

可以工作的类装饰器示例:

def my_deco(name):
    # define the decorator function that acts on the actual class definition
    def decorator(cls):

        # do something here with the information
        print name, cls

        setattr(class, name, 'Hello world!')

        # return the original, augmented class
        return cls

    # return the decorator to act on the class definition
    return decorator