尽管有很多关于将类用作装饰器的资源,但我找不到能处理装饰方法问题的资源。这个问题的目的是解决这个问题。我将发布自己的解决方案,但是当然也邀请其他所有人发布他们的解决方案。
标准装饰器类实现的问题是python不会创建装饰函数的绑定方法:
class Deco:
def __init__(self, func):
self.func= func
def __call__(self, *args):
self.func(*args)
class Class:
@Deco
def hello(self):
print('hello world')
Class().hello() # throws TypeError: hello() missing 1 required positional argument: 'self'
方法装饰者需要克服这一障碍。
以前面示例中的类为例,预期将完成以下工作:
>>> i= Class()
>>> i.hello()
hello world
>>> i.hello
<__main__.Deco object at 0x7f4ae8b518d0>
>>> Class.hello is Class().hello
False
>>> Class().hello is Class().hello
False
>>> i.hello is i.hello
True
理想情况下,函数__doc__
和签名以及类似属性也应保留。
通常,当方法访问为时some_instance.some_method()
,python的描述符协议会加入并调用some_method.__get__()
,这会返回绑定的方法。但是,由于该方法已被Deco
类的实例替换,因此不会发生-因为Deco
它不是描述符。为了Deco
按预期进行工作,它必须实现一个__get__
返回自身绑定副本的方法。
这是基本的“不执行任何操作”修饰符类:
import inspect
import functools
from copy import copy
class Deco(object):
def __init__(self, func):
self.__self__ = None # "__self__" is also used by bound methods
self.__wrapped__ = func
functools.update_wrapper(self, func)
def __call__(self, *args, **kwargs):
# if bound to an object, pass it as the first argument
if self.__self__ is not None:
args = (self.__self__,) + args
#== change the following line to make the decorator do something ==
return self.__wrapped__(*args, **kwargs)
def __get__(self, instance, owner):
if instance is None:
return self
# create a bound copy
bound = copy(self)
bound.__self__ = instance
# update __doc__ and similar attributes
functools.update_wrapper(bound, self.__wrapped__)
# add the bound instance to the object's dict so that
# __get__ won't be called a 2nd time
setattr(instance, self.__wrapped__.__name__, bound)
return bound
要使装饰器执行某些操作,请在__call__
方法中添加代码。
这是一个带有参数的参数:
class DecoWithArgs(object):
#== change the constructor's parameters to fit your needs ==
def __init__(self, *args):
self.args = args
self.__wrapped__ = None
self.__self__ = None
def __call__(self, *args, **kwargs):
if self.__wrapped__ is None:
return self.__wrap(*args, **kwargs)
else:
return self.__call_wrapped_function(*args, **kwargs)
def __wrap(self, func):
# update __doc__ and similar attributes
functools.update_wrapper(self, func)
return self
def __call_wrapped_function(self, *args, **kwargs):
# if bound to an object, pass it as the first argument
if self.__self__ is not None:
args = (self.__self__,) + args
#== change the following line to make the decorator do something ==
return self.__wrapped__(*args, **kwargs)
def __get__(self, instance, owner):
if instance is None:
return self
# create a bound copy of this object
bound = copy(self)
bound.__self__ = instance
bound.__wrap(self.__wrapped__)
# add the bound decorator to the object's dict so that
# __get__ won't be called a 2nd time
setattr(instance, self.__wrapped__.__name__, bound)
return bound
这样的实现使我们可以在方法和函数上使用装饰器,因此我认为应该将其视为良好实践。
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我来说两句