Python鏈式裝飾器覆蓋屬性

Question

我有兩個裝飾器。每個裝飾器都有一個作爲參數的函數。每個裝飾器爲該功能設置一個屬性。在單個函數上鍊接裝飾器之後，我希望看到2個新屬性。但是，頂級裝飾器t2會「覆蓋」屬性t1集合。否則，在解決所有問題後，t1不再存在。任何人都可以解釋爲什麼以及如何解決它？

def t1(function): 
def wrapper(*args, **kwargs): 
    setattr(wrapper, "t1", True) 
    return function(*args, **kwargs) 
setattr(wrapper, "t1", False) 
return wrapper 

def t2(function): 
def wrapper(*args, **kwargs): 
    setattr(wrapper, "t2", True) 
    return function(*args, **kwargs) 
setattr(wrapper, "t2", False) 
return wrapper 

@t2 
@t1 
def test(): 
pass 

Answer 1

碰巧，因爲你的裝飾器在包裝上設置了屬性。當第一個裝飾在它的包裝器上設置屬性時，它將包裝器傳遞給第二個裝飾器，它在第一個包裝器上添加另一個包裝器，並在第二個包裝器上設置屬性。所以你最終得到第二個包裝。

In [3]: def decorator_a(fn): 
    ...:  def wrapper(*args, **kwargs): 
    ...:   return fn(*args, **kwargs) 
    ...:  print("I'm setting the attribute on function {}".format(id(wrapper))) 
    ...:  setattr(wrapper, "attr1", True) 
    ...:  return wrapper 
    ...: 

In [4]: def decorator_b(fn): 
    ...:  def wrapper(*args, **kwargs): 
    ...:   return fn(*args, **kwargs) 
    ...:  print("I'm setting the attribute on function {}".format(id(wrapper))) 
    ...:  setattr(wrapper, "attr2", True) 
    ...:  return wrapper 
    ...: 

In [5]: first_time_decorated = decorator_a(lambda x: x) 
I'm setting the attribute on function 4361847536 

In [6]: second_time_decorated = decorator_b(first_time_decorated) 
I'm setting the attribute on function 4361441064 

您可以通過設置功能的所有屬性解決這個正在裝修的包裝

In [14]: def decorator_a(fn): 
    ...:  def wrapper(*args, **kwargs): 
    ...:   return fn(*args, **kwargs) 
    ...:  setattr(wrapper, "attr1", True) 
    ...:  for attribute in set(dir(fn)) - set(dir(wrapper)): 
    ...:   setattr(wrapper, attribute, getattr(fn, attribute)) 
    ...:  return wrapper 
    ...: 

In [15]: def decorator_b(fn): 
    ...:  def wrapper(*args, **kwargs): 
    ...:   return fn(*args, **kwargs) 
    ...:  setattr(wrapper, "attr2", True) 
    ...:  for attribute in set(dir(fn)) - set(dir(wrapper)): 
    ...:   setattr(wrapper, attribute, getattr(fn, attribute)) 
    ...:  return wrapper 
    ...: 

In [16]: first_time_decorated = decorator_a(lambda x: x) 

In [17]: second_time_decorated = decorator_b(first_time_decorated) 

In [18]: second_time_decorated.attr1 
Out[18]: True 

In [19]: second_time_decorated.attr2 
Out[19]: True