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how to make a decorator function to be part of class

By : Miriam Mugauri
Date : October 16 2020, 06:10 PM
will help you You can't use a decorator on a method where the decorator expression refers to an instance attribute. That's because decorators are executed when the function they decorate is being created. Inside a class statement body that means that when decorators are applied, there is no class yet, and without a class, there can't be any instances either.
You have two options:
code :
class Websocket:

    def __init__(self):
        self.eio = engineio.Client()
        self.eio.on('connect', self.on_connect)
        # don't call wait, see below

    def on_connect(self):
        print('connection established')
class Websocket:

    def __init__(self):
        self.eio = engineio.Client()

        def on_connect():
            print('connection established')

        # don't call wait, see below

but that makes it much harder to use that function directly from other code. 
class Websocket:
    def __init__(self, socket_url):
        self.eio = engineio.Client()
        self.eio.on('connect', self.on_connect)
        # other registrations

    def on_connect(self):
        # handle connection

    # other handlers

    def wait(self):

websocket = Websocket('http://localhost:5000)

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How to use Python Decorator to change only one part of function?

By : Hiesham Merhi
Date : March 29 2020, 07:55 AM
hop of those help? What do you think about using a separate function (as a private method) for list processing? For example, you may do the following:
code :
def __list_processing(self, list): 
    #do the generic processing of your lists

def list_expenses(self):
    #invoke __list_processing with self.expensedict as a parameter

def list_income(self):
    #invoke __list_processing with self.incomedict as a parameter

typescript class decorator: typing properties defined in decorator function

By : Daniel Toney
Date : March 29 2020, 07:55 AM
I hope this helps . Within the decorator target refers to the function—Foo—rather than the prototype—Foo.prototype.
So in the decorator doing target.inDecorator = ... is the same as Foo.inDecorator = ... and not Foo.prototype.inDecorator = ....
code :
interface BarStatic {
    new(): BarInstance;
    inDecorator: string;

interface BarInstance {
    inDecorator: string;

function bar(target: BarStatic) {
    target.inDecorator = 'static';
    // note that prototype will be `any` here though
    target.prototype.inDecorator = 'instance';

class Foo {
    static inDecorator: string; // required
    inDecorator: string;        // required
    inClass: string;

    constructor() {
        this.inClass = 'a string';

    getInClass() {
        return this.inClass;

console.log(Foo.inDecorator);           // static
console.log(Foo.prototype.inDecorator); // instance
const foo = new Foo();
console.log(foo.getInClass());          // a string
console.log(foo.inDecorator);           // instance

typescript class decorator can not access static value if decorator return as high order function

By : J. Ortega
Date : March 29 2020, 07:55 AM
To fix the issue you can do The way decorators work is that if you return a value from the decorator, that will replace the decorated class. The function you return can successfully replace Foo but since it does not inherit the properties of the original Foo it will not be available on the replaced Foo.
The simplest solution is to return an anonymous class that derives from the class that is passed to the decorator.
code :
function Bar(FooClass: typeof Foo) {
    console.log('in Bar decorator');
    return class extends FooClass {
        constructor(args: any) {
            console.log('in Bar high order function: ', args);

class Foo {

    a = 1;
    static b = 2;
    constructor(args: any) {
        console.log('in Foo constructor')
        console.log('Foo instance a: ', this.a);
        console.log('Foo static b: ', Foo.b);

new Foo(123);

How can I make a class decorator not break isinstance function?

By : user2577323
Date : March 29 2020, 07:55 AM
hope this fix your issue You can use the singleton class decorator in the Python Decorator Library.
It works because it modifies the existing class (replaces the __new__() method) instead of replacing it with a completely separate class as is being done in the code in your question.
code :
import functools

# from https://wiki.python.org/moin/PythonDecoratorLibrary#Singleton
def singleton(cls):
    ''' Use class as singleton. '''

    cls.__new_original__ = cls.__new__

    def singleton_new(cls, *args, **kw):
        it =  cls.__dict__.get('__it__')
        if it is not None:
            return it

        cls.__it__ = it = cls.__new_original__(cls, *args, **kw)
        it.__init_original__(*args, **kw)
        return it

    cls.__new__ = singleton_new
    cls.__init_original__ = cls.__init__
    cls.__init__ = object.__init__

    return cls
[2, 3, 4, 5, 6, 0, 1, 2, 3, 4]
[5, 6, 0, 1, 2]
[3, 4, 5, 6, 0, 1, 2]
<class '__main__.Counter'>
<class '__main__.Counter'>

Limit of decorator as class compared to decorator as function

By : Sylar
Date : March 29 2020, 07:55 AM
like below fixes the issue I want to make sure that I understood correctly how decorator as class works. , You could write an equivalent class-based decorator like this...
code :
class addx:
    def __new__(self, obj):
        obj.x = 10
        return obj

class A:

assert A.x == 10
def addx_func(kls):
    def wrapper():
        res = kls()
        res.x = 10
        return res

    return wrapper

class addx_class:
    def __init__(self, kls):
        self.kls = kls

    def __call__(self):
        res = self.kls()
        res.x = 10
        return res

class A:

class B:

a = A()
assert a.x == 10

b = B()
assert b.x == 10
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