多个Python装饰器

Question

我有一个带有装饰方法 (my_method) 的 Django 模型 (MyModel)。我希望装饰器对 my_method 执行一些检查：

• 如果检查成功，my_method 应该返回一个字符串；

• 如果检查不成功，my_method 应该返回装饰器返回的失败消息。

逻辑如下：

# models.py
class MyModel(models.Model):
    @decorator1
    @decorator2
    def my_method(self, request, *args, **kwargs):
        return u'The result that must be returned if all the checks performed by the decorator succeed'


# decorators.py
from functools import wraps

# decorator1 checks if certain conditions are met. If yes, it returns the decorated method (method_to_decorate); if not, it returns a tuple
def decorator1(method_to_decorate):
    @wraps(method_to_decorate)
    def wrapper1(self, request, *args, **kwargs):
        if a_condition :
            return method_to_decorate(self, request, *args, **kwargs)
        else:
            # we return a failure message
            return ('failure', 'message') 
    return wrapper1

# in decorator2, we want to know if the check performed by decorator1 was successful
# in case of success, we perform decorator2's check
# in case of failure, decorator2 should simply pass the failure message returned by decorator1   
def decorator2(method_to_decorate):
    @wraps(method_to_decorate)
    def wrapper2(self, request, *args, **kwargs):

        # if the first decorator succeeded
        if decorator1_s_test_was_successful:
            # we check if the conditions of the second decorator are met
            if decorator2_s_test_was_successful:
                # we return the method
                return method_to_decorate(self, request, *args, **kwargs)
            else:
                # we return a failure message
                return ('another failure', 'message')
    # if the first decorator did not succeed
        else: # decorator1 returned a tuple : ('failure', 'message') 
            return the_failure_that_decorator1_returned  
    return wrapper2

因此，如果decorator1返回失败，我期望 an_instance_of_my_model_instance.my_method(request) 返回('failure', 'message')。如果decorator1成功但decorator2失败，我会期望（'另一个失败'，'消息'）。如果所有测试都通过了，u'如果装饰器执行的所有检查都成功则必须返回的结果'

如果decorator1的检查成功通过，我不知道如何检查decorator2。我尝试通过检查decorator2中method_to_decorate的type()来做到这一点，但似乎type使用原始方法本身，而不是decorator1返回的结果（就好像装饰器不知道以前的装饰器执行的操作一样） 。

先感谢您！

Answer 1

装饰器将按照您将它们放在装饰方法上方的顺序进行调用，并且考虑到您的程序结构，如果失败decorator2则不会被调用decorator1，因此无需检查.decorator1decorator2

一个稍微简单一点的例子......

from functools import wraps


def decorator1(f):
    @wraps(f)
    def wrapper(a):
        if a >= 1:
            return f(a)
        return 'failed in decorator 1'
    return wrapper

def decorator2(f):
    @wraps(f)
    def wrapper(a):
        if a >= 2:
            return f(a)
        return 'failed in decorator 2'
    return wrapper

@decorator1
@decorator2
def my_func(a):
    return 'success'


print my_func(0)
print my_func(1)
print my_func(2)

...打印...

failed in decorator 1
failed in decorator 2
success

Answer 2

如果您想检查返回的内容，则需要交换和行：@decorator1@decorator2decorator2decorator1

@decorator2
@decorator1
def my_method(self, request, *args, **kwargs):
    return u'The result that must be returned if all the checks performed by the decorator succeed'

现在decorator2将包装返回的任何方法decorator1，因此您可以检查该方法返回的内容。

def decorator2(method_to_decorate):
    @wraps(method_to_decorate)
    def wrapper2(self, request, *args, **kwargs):

        result = method_to_decorate(self, request, *args, **kwargs)

        if isinstance(result, tuple) and result and result[0] == 'failure':
            # decorator1 returned a failure
            return result
        else:
            # decorator1 passed through the wrapped method call
            if decorator2_s_test_was_successful:
                return result
            else:
                return ('another failure', 'message')

    return wrapper2