python - 我可以从 python 中的方法装饰器编辑类变量吗?
问题描述
我有一堂课如下:
class Hamburger():
topping_methods = {}
@prepare_topping("burger", "onion_ring")
def cook(self, stuff, temp):
print("cooking")
h = Hamburger()
我希望 prepare_topping 装饰器添加条目Hamburger.topping_methods
,使其看起来像:
{"burger":< cook method reference >, "onion_ring": < cook method reference >}
关键是我需要在类的初始化程序运行之前发生这种情况(真正的用例是 dict 用于在初始化程序中注册事件回调。)但是因为我想访问类变量,它需要在定义类之后。
这是我对装饰器逻辑的了解:
def prepare_topping(*args):
def deco(func):
# This is when I want to add to class dict, but cannot access method arguments yet
print(eval(func.__qualname__.split(".")[0]).topping_methods) # Gets class that method belongs to in a hacky way, but the class is not yet defined
def wrapper(self, *args):
print(self.topping_methods) # Only run if the method is called, which is after __init__
return func(self, *args)
return wrapper
return deco
我意识到我将永远无法访问方法self
参数来实现这一点,因为无论该方法是否实际被调用,我都想做一些事情。有没有一种方法可以让装饰器仅在定义类之后运行?在仍然使用装饰器的同时还有其他方法可以实现这一点吗?
解决方案
您可以使用超类和__init_subclass__
挂钩来连接:
class CookeryClass:
topping_methods: dict
def __init_subclass__(cls, **kwargs):
cls.topping_methods = {}
for obj in vars(cls).values():
if hasattr(obj, "topping_keys"):
for key in obj.topping_keys:
cls.topping_methods[key] = obj
def prepare_topping(*keys):
def decorator(func):
func.topping_keys = keys
return func
return decorator
class Hamburger(CookeryClass):
@prepare_topping("burger", "onion_ring")
def cook(self, stuff, temp):
print("cooking")
@prepare_topping("mayonnaise", "pineapples")
def not_on_a_pizza_surely(self, stuff, temp):
print("cooking")
print(Hamburger.topping_methods)
这打印出来
{
'burger': <function Hamburger.cook at 0x000001EA49D293A0>,
'onion_ring': <function Hamburger.cook at 0x000001EA49D293A0>,
'mayonnaise': <function Hamburger.not_on_a_pizza_surely at 0x000001EA49D29430>,
'pineapples': <function Hamburger.not_on_a_pizza_surely at 0x000001EA49D29430>,
}