带有自我参数的类方法装饰器?

小开

你不能。类体中没有self，因为不存在实例。你需要传递给它，比如说，一个包含属性名的str来查找实例，然后返回的函数可以这样做，或者使用完全不同的方法。

小开

最佳答案

是的。不是在类定义时传入实例属性，而是在运行时检查它:

def check_authorization(f):
def wrapper(*args):
print args[0].url
return f(*args)
return wrapper


class Client(object):
def __init__(self, url):
self.url = url


@check_authorization
def get(self):
print 'get'


>>> Client('http://www.google.com').get()
http://www.google.com
get

装饰器截取方法参数;第一个参数是实例，因此它从实例中读取属性。如果你不想硬编码属性名，你可以将属性名作为字符串传递给装饰器，并使用getattr:

def check_authorization(attribute):
def _check_authorization(f):
def wrapper(self, *args):
print getattr(self, attribute)
return f(self, *args)
return wrapper
return _check_authorization

小开

from re import search
from functools import wraps


def is_match(_lambda, pattern):
def wrapper(f):
@wraps(f)
def wrapped(self, *f_args, **f_kwargs):
if callable(_lambda) and search(pattern, (_lambda(self) or '')):
f(self, *f_args, **f_kwargs)
return wrapped
return wrapper


class MyTest(object):


def __init__(self):
self.name = 'foo'
self.surname = 'bar'


@is_match(lambda x: x.name, 'foo')
@is_match(lambda x: x.surname, 'foo')
def my_rule(self):
print 'my_rule : ok'


@is_match(lambda x: x.name, 'foo')
@is_match(lambda x: x.surname, 'bar')
def my_rule2(self):
print 'my_rule2 : ok'






test = MyTest()
test.my_rule()
test.my_rule2()

< p >输出: My_rule2: ok

小开

一个更简洁的例子如下:

#/usr/bin/env python3
from functools import wraps


def wrapper(method):
@wraps(method)
def _impl(self, *method_args, **method_kwargs):
method_output = method(self, *method_args, **method_kwargs)
return method_output + "!"
return _impl


class Foo:
@wrapper
def bar(self, word):
return word


f = Foo()
result = f.bar("kitty")
print(result)

这将打印:

kitty!

小开

另一种选择是放弃语法糖，并在类的__init__中进行装饰。

def countdown(number):
def countdown_decorator(func):
def func_wrapper():
for index in reversed(range(1, number+1)):
print(index)
func()
return func_wrapper
return countdown_decorator


class MySuperClass():
def __init__(self, number):
self.number = number
self.do_thing = countdown(number)(self.do_thing)
    

def do_thing(self):
print('im doing stuff!')




myclass = MySuperClass(3)


myclass.do_thing()

它会打印

3
2
1
im doing stuff!

小开

我知道这是一个老问题，但这个解决方案还没有被提及，希望它可以帮助到今天的人，8年后。

那么，包装包装呢?让我们假设不能更改装饰器和将这些方法装饰在init中(它们可能是@property decoration或其他)。总是有可能创建自定义的、特定于类的装饰器，该装饰器将捕获self并随后调用原始的装饰器，并将运行时属性传递给它。

下面是一个工作示例(f-string需要python 3.6):

import functools


# imagine this is at some different place and cannot be changed
def check_authorization(some_attr, url):
def decorator(func):
@functools.wraps(func)
def wrapper(*args, **kwargs):
print(f"checking authorization for '{url}'...")
return func(*args, **kwargs)
return wrapper
return decorator


# another dummy function to make the example work
def do_work():
print("work is done...")


###################
# wrapped wrapper #
###################
def custom_check_authorization(some_attr):
def decorator(func):
# assuming this will be used only on this particular class
@functools.wraps(func)
def wrapper(self, *args, **kwargs):
# get url
url = self.url
# decorate function with original decorator, pass url
return check_authorization(some_attr, url)(func)(self, *args, **kwargs)
return wrapper
return decorator
        

#############################
# original example, updated #
#############################
class Client(object):
def __init__(self, url):
self.url = url
    

@custom_check_authorization("some_attr")
def get(self):
do_work()


# create object
client = Client(r"https://stackoverflow.com/questions/11731136/class-method-decorator-with-self-arguments")


# call decorated function
client.get()

输出:

checking authorisation for 'https://stackoverflow.com/questions/11731136/class-method-decorator-with-self-arguments'...
work is done...

小开

我知道这个问题已经很老了，但是下面的解决方法以前没有人提过。这里的问题是你不能在类块中访问self，但你可以在类方法中访问。

让我们创建一个虚拟装饰器来多次重复一个函数。

import functools
def repeat(num_rep):
def decorator_repeat(func):
@functools.wraps(func)
def wrapper_repeat(*args, **kwargs):
for _ in range(num_rep):
value = func(*args, **kwargs)
return
return wrapper_repeat
return decorator_repeat

class A:
def __init__(self, times, name):
self.times = times
self.name = name
    

def get_name(self):
@repeat(num_rep=self.times)
def _get_name():
print(f'Hi {self.name}')
_get_name()

小开

拥有一个通用实用程序将非常有用，它可以将函数的任何 decorator转换为方法的decorator。我想了一个小时，终于想出了一个:

from typing import Callable
Decorator = Callable[[Callable], Callable]


def decorate_method(dec_for_function: Decorator) -> Decorator:


def dec_for_method(unbounded_method) -> Callable:
# here, `unbounded_method` will be a unbounded function, whose
# invokation must have its first arg as a valid `self`. When it
# return, it also must return an unbounded method.
def decorated_unbounded_method(self, *args, **kwargs):
@dec_for_function
def bounded_method(*args, **kwargs):
return unbounded_method(self, *args, **kwargs)
return bounded_method(*args, **kwargs)


return decorated_unbounded_method


return dec_for_method

用法是:

# for any decorator (with or without arguments)
@some_decorator_with_arguments(1, 2, 3)
def xyz(...): ...


# use it on a method:
class ABC:
@decorate_method(some_decorator_with_arguments(1, 2, 3))
def xyz(self, ...): ...

测试:

def dec_for_add(fn):
"""This decorator expects a function: (x,y) -> int.


If you use it on a method (self, x, y) -> int, it will fail at runtime.
"""
print(f"decorating: {fn}")
def add_fn(x,y):
print(f"Adding {x} + {y} by using {fn}")
return fn(x,y)
return add_fn




@dec_for_add
def add(x,y):
return x+y


add(1,2)  # OK!




class A:
@dec_for_add
def f(self, x, y):
# ensure `self` is still a valid instance
assert isinstance(self, A)
return x+y


# TypeError: add_fn() takes 2 positional arguments but 3 were given
# A().f(1,2)
    



class A:
@decorate_method(dec_for_add)
def f(self, x, y):
# ensure `self` is still a valid instance
assert isinstance(self, A)
return x+y


# Now works!!
A().f(1,2)