代码之家 › 专栏 › 技术社区 › Lokesh Agrawal

类级装饰器何时装饰?

python-internals python

Lokesh Agrawal · 技术社区 · 7 年前

def debug(func):
    msg = func.__name__

    @wraps(func)
    def wrapper(*args, **kwargs):
        print(msg)
        return func(*args, **kwargs)
    return wrapper 

# Decorator for all the methods in a class
def debugmethods(cls):
    for key, val in vars(cls).items():
        if callable(val):
            setattr(cls, key, debug(val))
    return cls

@debugmethods
class Spam:
    def foo(self):
        pass

    def bar(self):
        pass

现在我正试图了解这是如何工作的,我的意思是什么时候装修会发生,我如何检查?

b) 当我第一次访问垃圾邮件类时?例如。

for key, val in Spam.__dict__.items():
        print(key, val)

c) 当我第一次实例化垃圾邮件类时?例如。

 spam = Spam()
 for key, val in Spam.__dict__.items():
     print(key, val)

1 回复 | 直到 7 年前

r.ook jpp 7 年前

如果您添加几行打印行,这实际上很容易在操作中看到:

print('Deocrator is being defined')
def deco(cls):
    print('Decorator is called')
    cls.decorated = True
    return cls

print('Foo is being defined')
@deco
class Foo:
    print('Foo class attributes are being set')
    def __init__(self):
        print('Foo is being instantiated')

print('Foo class is being referenced in main script')
print(f'Foo is decorated: {Foo.decorated}')
print('Foo instance is being created in main script')
print(Foo())

Deocrator is being defined
Foo is being defined
Foo class attributes are being set
Decorator is called    # <--- decoration happens immediately after definition of Foo
Foo class is being referenced in main script
Foo is decorated: True
Foo instance is being created in main script
Foo is being instantiated
<__main__.Foo object at 0x00789150>

简言之,答案很像@jornsharpe所说的,它已经发生了。只是想想视觉效果会有帮助。

推荐文章

Tim unnamed eng · 在“C.\uu dict\uuu2”的输出中,“C”对象的“属性”xxx”是什么意思?

8 年前