如何为 class 定义一个装饰器来装饰 class 方法

Question

I want add some fixed vars to the class method. But I did not want to pass those vars every time when using it. I cannot decorate the class method directly, because my class is a child class and I cannot modify the parent class. Here is what I want to try:

def callable(o):
    return hasattr(o, "__call__")

def trace(f):
    def traced(*args, **kw):
        "Print message before and after a function call."
        print("Entering", f.__name__)
        kw['new value'] = 'new value'
        result = f(*args, **kw)
        print("Leaving", f.__name__)
        return result
    return traced

def mtrace(cls):
    for key, val in cls.__dict__.items():
        if key.startswith("__") and key.endswith("__") or not callable(val):
            continue
        print('calling in mtrace', key)
        setattr(cls, key, trace(val))
        print("Wrapped", key)
    return cls


class dull:

    @classmethod
    def method1(cls, **arg):
        print("Method 1 called with arg", arg)

@mtrace
class myclass(dull):pass


myclass.method1(a='hello')

output is:

try class method
Method 1 called with arg {'a': 'hello'}

the new value is not add to the method1. I am not quite understand how the class method is called by the python interpreter. Thanks a lot if anyone can help me.

Answer 1

I try use super to redefine the parent class. It works as I want. But I didnot use a decorator. But It doesn't look pretty.

class BaseRequest:  # cannot modify this class

    @classmethod
    def http_get(cls, *vars, **kws):
        print("Method 1 called with arg", kws)

class MyRequest(BaseRequest):
    extra_vars = {}

    @classmethod
    def http_get(cls, *vars, **kws):
        kws.update(cls.extra_vars)
        super().http_get(*vars, **kws)

    @classmethod
    def set_extra_vars(cls, **kws):
        cls.extra_vars.update(kws)

MyRequest.set_extra_vars(header='my hearders')
MyRequest.http_get(a='hello')

Out put Method 1 called with arg {'a': 'hello', 'header': 'my hearders'}