[英]How to add methods of class to a list inside the class with a decorator
I would like to update a "class-wide" list from a decorator that decorates the class' methods and adds each decorated method to that list. 我想从装饰器更新一个“全类”列表,该装饰器装饰该类的方法并将每个装饰的方法添加到该列表中。
This is what came to mind: 这是我想到的:
def add(meth: callable):
Spam.eggs.append(func)
return meth
class Spam:
eggs = []
@add
def meth(self):
pass
This won't work though because Spam
hasn't finished defining itself when @add
is reached, and thus add
raises a NameError
, as pointed out in the comments. 不过这不会起作用,因为到达
@add
时, Spam
尚未完成自身的定义,因此add
会引发NameError
,如注释中所指出。
I also tried a class method: 我也尝试了一个类方法:
class Spam:
eggs = []
@classmethod
def add(cls, meth: callable):
cls.eggs.append(meth)
return meth
@add
def meth(self):
pass
But this doesn't work either because when @add
is reached, add
is bound to the classmethod
decorated instance, which is not callable. 但这也不起作用,因为到达
@add
时, add
绑定到装饰了classmethod
实例,该实例不可调用。
Here is what I need this for: 这是我需要的:
I have a class with several methods that take one argument (besides self
) that transform that object in such a way that these methods may be composed with one another. 我有一类带有几种方法的类,这些方法采用一个参数(
self
除外),该参数以一种可以使这些方法相互组合的方式转换该对象。 I want to decorate each of these in such a way that they're automatically added to a list in the class. 我想以一种将它们自动添加到该类列表中的方式来装饰它们。
Eg: 例如:
from typing import List
def transform_meth(meth: callable):
TextProcessor.transforms.add(meth)
return meth
class TextProcessor:
transforms: List[callable] = []
@transform_meth
def m1(self, text):
return text
@transform_meth
def m2(self, text):
return text
def transform(self, text):
for transform in self.transforms:
text = transform(text)
return text
I could add the methods in the list manually, but I find the decorator to be clearer since it is close to the definition of the method, and thus it is easier to remember to decorate a new method when defining it than adding it to the list manually. 我可以手动将方法添加到列表中,但是我发现装饰器更加清晰,因为它与方法的定义很接近,因此与定义新方法相比,记住它来装饰新方法要容易得多。手动。
Your current approach fails because when transform_meth
is called, TextProcessor
isn't bound to anything yet (or if it is, that object gets overwritten when the class
statement completes). 您当前的方法失败了,因为调用了
transform_meth
时, TextProcessor
尚未绑定到任何对象(或者如果绑定了,则在class
语句完成时该对象将被覆盖)。
The simple solution would be to define transform_meth
inside the class
statement, so that it could simply declare transforms
as a nonlocal variable. 一种简单的解决方案是在
class
语句内定义transform_meth
,这样它就可以简单地transforms
声明为一个非局部变量。 However, that won't work because a class
statement doesn't establish a new scope. 但是,这将不起作用,因为
class
语句未建立新的作用域。
Instead, you can define a function that creates the decorator, which takes the desired list (at that point a just a name in the body of the class
statement, not from any assumed scope). 相反,您可以定义一个创建装饰器的函数,该装饰器将获取所需的列表(此时,
class
声明主体中仅是一个名称,而不是来自任何假定的范围)。 That function returns a closure over the list argument so that you can append to it. 该函数在list参数上返回一个闭包,以便您可以附加到它。
def make_decorator(lst):
# *This* will be the function bound to the name 'transform_meth'
def _(meth):
lst.append(meth)
return meth
return _
class TextProcessor:
transforms: List[callable] = []
transform_meth = make_decorator(transforms)
@transform_meth
def m1(self, text):
return text
@transform_meth
def m2(self, text):
return text
def transform(self, text):
for transform in self.transforms:
text = transform(text)
return text
del transform_meth # Not needed anymore, don't create a class attribute
Since the arg of each method is self you can append to the object instance like so: 由于每个方法的arg是self,因此可以将其附加到对象实例,如下所示:
from functools import wraps
def appender(f):
@wraps(f)
def func(*args, **kwargs):
if f not in args[0].transforms:
args[0].transforms.append(f)
return f(*args, **kwargs)
return func
class Foo(object):
def __init__(self):
self.transforms = []
@appender
def m1(self, arg1):
return arg1
@appender
def m2(self, arg1):
return arg1
def transform(self, text):
methods = [f for f in dir(self) if not f.startswith("__") and callable(getattr(self,f)) and f != 'transform']
for f in methods:
text = getattr(self,f)(text)
return text
f = Foo()
f.transform('your text here')
print(f.transforms)
Output: 输出:
[<function Foo.m1 at 0x1171e4e18>, <function Foo.m2 at 0x1171e4268>]
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