Breaking News: Grepper is joining You.com. Read the official announcement!

one instance class python

Yasha answered on September 7, 2022 Popularity 7/10 Helpfulness 10/10

answer one instance class python

one instance class python

Comment

### USING __new__ 
class Singleton(object):
     def __new__(cls, *args, **kw):
         if not hasattr(cls, '_instance'):
             orig = super(Singleton, cls)
             cls._instance = orig.__new__(cls, *args, **kw)
         return cls._instance

 class MyClass(Singleton):
     a = 1

 one = MyClass()
 two = MyClass()

 two.a = 3
 print one.a
 #3
 print id(one)
 #29097904
 print id(two)
 #29097904
 print one == two
 #True
 print one is two
 #True

## USING __metaclass__
class Singleton2(type):
    def __init__(cls, name, bases, dict):
        super(Singleton2, cls).__init__(name, bases, dict)
        cls._instance = None

    def __call__(cls, *args, **kw):
        if cls._instance is None:
            cls._instance = super(Singleton2, cls).__call__(*args, **kw)
        return cls._instance


    class MyClass2(object):
        __metaclass__ = Singleton2

    one = MyClass2()
    two = MyClass2()

    two.a = 3
    print one.a
    #3
    print id(one)
    #31495472
    print id(two)
    #31495472
    print one == two
    #True
    print one is two
    #True

## USING DECORATOR
def singleton(cls, *args, **kw):
     instances = {}
     def _singleton(*args, **kw):
        if cls not in instances:
             instances[cls] = cls(*args, **kw)
        return instances[cls]
     return _singleton

 @singleton
 class MyClass3(object):
     a = 1
     def __init__(self, x=0):
         self.x = x

 one = MyClass3()
 two = MyClass3()

 two.a = 3
 print one.a
 #3
 print id(one)
 #29660784
 print id(two)
 #29660784
 print one == two
 #True
 print one is two
 #True
 one.x = 1
 print one.x
 #1
 print two.x
 #1

Popularity 7/10 Helpfulness 10/10 Language python

Source: stackoverflow.com

Tags: class instance python

Link to this answer
Share Copy Link

Contributed on Sep 07 2022

Yasha

0 Answers Avg Quality 2/10

one instance class python

Contents

More Related Answers

one instance class python

Grepper

Documentation

Social

Legal

Contact

Oops, You will need to install Grepper and log-in to perform this action.