解析装饰器中的 args 和 kwargs

我有一个需要 args 和 kwargs 的函数，我需要根据 args 和 kwargs 的值在我的装饰器中做一些事情2nd函数中的arg，如下面的代码所示：

def workaround_func():
    def decorator(fn):
        def case_decorator(*args, **kwargs):
            if args[1] == 2:
                print('The second argument is a 2!')
            return fn(*args, **kwargs)
        return case_decorator
    return decorator

@workaround_func()
def my_func(arg1, arg2, kwarg1=None):
    print('arg1: {} arg2: {}, kwargs: {}'.format(arg1, arg2, kwarg1))

问题是 python 允许用户使用第二个参数作为常规参数或关键字参数来调用函数，因此如果用户调用my_func with arg2作为一个 kwarg，它提出了IndexError， 见下文：

In [8]: d.my_func(1, 2, kwarg1=3)
The second argument is a 2!
arg1: 1 arg2: 2, kwargs: 3

In [9]: d.my_func(1, arg2=2, kwarg1=3)
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-9-87dc89222a9e> in <module>()
----> 1 d.my_func(1, arg2=2, kwarg1=3)

/home/camsparr/decoratorargs.py in case_decorator(*args, **kwargs)
      2     def decorator(fn):
      3         def case_decorator(*args, **kwargs):
----> 4             if args[1] == 2:
      5                 print('The second argument is a 2!')
      6             return fn(*args, **kwargs)

IndexError: tuple index out of range

有没有办法解决这个问题而不只是做try/except并抓住IndexError?

我使用 python 找到了答案decorator https://github.com/micheles/decorator包裹。该包的一个功能是，无论用户如何传递位置/关键字参数，它都会保留它们。它的额外好处是减少了大量代码，所以我的原始代码：

def workaround_func():
    def decorator(fn):
        def case_decorator(*args, **kwargs):
            if args[1] == 2:
                print('The second argument is a 2!')
            return fn(*args, **kwargs)
        return case_decorator
    return decorator

@workaround_func()
def my_func(arg1, arg2, kwarg1=None):
    print('arg1: {} arg2: {}, kwargs: {}'.format(arg1, arg2, kwarg1))

becomes:

from decorator import decorator

@decorator
def workaround_decorator(f, *args, **kwargs):
    if args[1] == 2:
        print('The second argument is 2!')
    return f(*args, **kwargs)

@workaround_decorator
def my_func(arg1, arg2, kwarg1=None):
    print('arg1: {} arg2: {}, kwargs: {}'.format(arg1, arg2, kwarg1))