python - "Unwraping"并在元类中再次包装@staticmethod

Question

我想创建元类，它将用跟踪装饰器装饰每个函数。

所以我得到了这个:

from functools import wraps
from inspect import getfile

from arrow import now


def trace(f):
    @wraps(f)
    def wrapper(*args, **kwargs):
        print(
            '{timestamp} - {file} - {function} - CALL *{args} **    {kwargs}'.format(timestamp=now().isoformat(sep=' '),
                                                                                                 file=getfile(f),
                                                                                 function=f.__name__, args=args[1:],
                                                                                 kwargs=kwargs))
        result = f(*args, **kwargs)
        print(
            '{timestamp} - {file} - {function} - RESULT     {result}'.format(timestamp=now().isoformat(sep=' '),
                                                                         file=getfile(f),
                                                                         function=f.__name__,
                                                                         result=result))
        return result

    return wrapper


class TraceLogger(type):
    def __new__(mcs, name, bases, dct):
        for attr in dct:
            value = dct[attr]
            if callable(value):
                dct[attr] = trace(value)
        return super(TraceLogger, mcs).__new__(mcs, name, bases, dct)


class ExampleClass(object):
    __metaclass__ = TraceLogger

    def foo(self):
        print('foo')

    @staticmethod
    def bar():
        print('bar')

example = ExampleClass()
example.foo()
example.bar()

跟踪适用于任何非静态函数，因为静态方法不可调用。如何解开 staticmethod 然后将其包装在 new metclass 中两次，如下所示:

dct[attr] = staticmethod(trace(value))

Answer 1

您可以通过调用 __get__ 来解开 staticmethod 对象。

@staticmethod
def func(*args):
    print('func called:', args)
    return 42

print(func)
print(func.__get__(None, object))
print(func.__get__(None, object)(1, 2, 3))

它输出:

<staticmethod object at 0x7f8d42835ac0>
<function func at 0x7f8d429561f0>
func called: (1, 2, 3)
42

至于为什么会这样，你可能有兴趣了解描述符协议(protocol)是什么，我推荐this link .