在调用之前检测方法是否被装饰

Question

我写了一个Python流程控制框架，其工作方式与unittest.TestCase非常相似：用户创建一个从框架class派生的class，然后编写自定义task_*(self) 方法。框架发现并运行它们：

###################
# FRAMEWORK LIBRARY
###################
import functools

class SkipTask(BaseException):
    pass

def skip_if(condition):
    def decorator(task):
        @functools.wraps(task)
        def wrapper(self, *args, **kargs):
            if condition(self):
                raise SkipTask()
            return task(self, *args, **kargs)
        return wrapper
    return decorator

class MyFramework(object):
    def run(self):
        print "Starting task"
        try:
            self.task()
        except SkipTask:
            print "Skipped task"
        except Exception:
            print "Failed task"
            raise
        else:
            print "Finished task"

#############
# USER SCRIPT
#############
class MyUserClass(MyFramework):
    skip_flag = True

    @skip_if(lambda self: self.skip_flag)
    def task(self):
        print "Doing something"

if __name__ == '__main__':
    MyUserClass().run()

输出：

Starting task
Skipped task

我想更改框架，以便在 @skip_if 的条件为 True 时，包装器不会打印 "Starting task"。我试过这个，但它不起作用：

def skip_if(condition):
    def decorator(task):
        print "decorating "  + str(task)
        task.__skip_condition = condition
        return task
    return decorator

class MyFramework(object):
    def run(self):
        try:
            if self.task.__skip_condition():
                print "Skipped task"
                return
        except AttributeError:
            print str(self.task) + " is not decorated"
            pass

        print "Starting task"
        try:
            self.task()
        except Exception as e:
            print "Failed task: " + str(e)
            raise
        else:
            print "Finished task"

输出：

decorating <function task at 0x194fcd70>
<bound method MyUserClass.task of <__main__.MyUserClass object at 0x195010d0>> is not decorated
Starting task
Doing something
Finished task

为什么没有跳过任务？

Answer 1

您正在使用双下划线名称，它在run方法中经过了private name mangling。

单步执行调试器时，我得到：

AttributeError: "'function' object has no attribute '_MyFramework__skip_condition

这里不要使用双下划线名称；如果您将函数属性重命名为 _skip_condition，则代码有效（前提是您绑定条件函数或显式传入 self）：

def skip_if(condition):
    def decorator(task):
        print "decorating "  + str(task)
        task._skip_condition = condition
        return task
    return decorator

class MyFramework(object):
    def run(self):
        try:
            if self.task._skip_condition(self):
                print "Skipped task"
                return
        except AttributeError:
            print str(self.task) + " is not decorated"
            pass

        print "Starting task"
        try:
            self.task()
        except Exception as e:
            print "Failed task: " + str(e)
            raise
        else:
            print "Finished task"

经过这些更改，输出变为：

decorating <function task at 0x1071a1b90>
Skipped task

在调用之前检测方法是否被装饰

Detect if method is decorated before invoking it

python

decorator

python-decorators