python进阶之装饰器之4在类中定义装饰器，将装饰器定义为类，两者的区别与联系

4.1 在类中定义装饰器

      以实例或者以类方法的形式进行应用

代码解析：

from functools import wraps

class A:
    # Decorator as an instance method
    def decorator1(self, func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            print('Decorator 1')
            return func(*args, **kwargs)
        return wrapper

    # Decorator as a class method
    @classmethod
    def decorator2(cls, func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            print('Decorator 2')
            return func(*args, **kwargs)
        return wrapper
    
    
# As an instance method
a = A()
@a.decorator1
def spam():
    pass


# As a class method
@A.decorator2
def grok():
    pass



# 这种方法在标准库中就有示例，比如说@property，实际是拥有
# getter()/setter()/deleter()方法的类，类中每一个定义的方
# 法可以作为装饰器
# 比如代码如下：
class Person:
    # Create a property instance
    first_name = property()

    # Apply decorator methods
    @first_name.getter
    def first_name(self):
        return self._first_name

    @first_name.setter
    def first_name(self, value):
        if not isinstance(value, str):
            raise TypeError('Expected a string')
        self._first_name = value

4.2 把装饰器定义为类

定义中需要实现__call__(),__get__() 方法

# 把装饰器定义为类
# 定义中需要实现__call__(),__get__() 方法


import types
from functools import wraps
class Profiled:
    def __init__(self, func):
        wraps(func)(self)
        self.ncalls = 0

    def __call__(self, *args, **kwargs):
        self.ncalls += 1
        return self.__wrapped__(*args, **kwargs)

    def __get__(self, instance, cls):
        if instance is None:
            return self
        else:
            return types.MethodType(self, instance)

# 在类外使用装饰器
@Profiled
def add(x, y):
    return x + y

# 在类中使用装饰器
class Spam:
    @Profiled
    def bar(self, x):
        print(self, x)


print(add(2, 3))    #5
print(add(3, 3))    #6
print(add(4, 3))    #7
print(add.ncalls)   #3



s = Spam()
print(s.bar(1))         #<__main__.Spam object at 0x000001F39D74D4E0> 1
print(s.bar(2))         #<__main__.Spam object at 0x000001F39D74D4E0> 2
print(s.bar(3))         #<__main__.Spam object at 0x000001F39D74D4E0> 3
print(Spam.bar.ncalls)  #3
print(s.bar.ncalls)     #3