详解Python装饰器的四种定义形式

def decorate(f):
    def wrapper(*args):
        return f(*args)*2
    return wrapper

@decorate
def add(a, b):
	return a + b

def test_decorate():
	sum = add(3, 5)
	assert sum == 16

def singleton(cls):
    instances = {}
    def wrapper(*args, **kwargs):
        if cls not in instances:
          instances[cls] = cls(*args, **kwargs)
        return instances[cls]
    return wrapper

@singleton
class MyClass:
    def method(self):
        pass

obj = MyClass()  # creates a new instance
obj2 = MyClass()  # returns the same instance
obj3 = MyClass()  # returns the same instance
...

class Star:
    def __init__(self, n):
        self.n = n

    def __call__(self, fn):
        @wraps(fn)
        def wrapper(*args, **kwargs):
            result = fn(*args, **kwargs)
            return result
        return wrapper

@Star(5)
def add(a, b):
    return a + b

class MyDecorator:
    def __init__(self, function):
        self.function = function
     
    def __call__(self, *args, **kwargs):
 
        # We can add some code
        # before function call
 
        self.function(*args, **kwargs)
 
        # We can also add some code
        # after function call.
# adding class decorator to the function
@MyDecorator
def function(name, message ='Hello'):
    print("{}, {}".format(message, name))

class MyClassDecorator(object):
	_instances = dict()

	def __init__(self, name):
		pass

	def __call__(self, cls):
		class WrappedClass(cls):
			def say_hello(self):
				print(f'Hello: {self.username}')
		return WrappedClass

@MyClassDecorator('test')
class MyClass():
	def __init__(self, username):
		self.username = username

def test_decoratorforclass():
	obj = MyClass('user1')
	obj.say_hello()