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Summary: singleton mode ensures that there is only one instance of a class and provides a global access point to it. Applicable when there can be only one instance of a class and customers can access it from a well-known access point, such as database, MQ, and so on.

Implementation method:

1. Realized by importing module

2. Realized by decorator.

3. Through the use of classes

4. Realized by _ _ new__ method

Source code to be imported in singleton module mode: singleton.py

#-*-coding: utf-8-*-# time: 2022-5-17 10file: singleton.py# author: tom# official account: play Test Development class Singleton (object): def _ init__ (self, name): self.name = name def run (self): print (self.name) s = Singleton ("Tom")

Main function source code:

#-*-coding: utf-8-*-# time: 2022-5-17 10 file 5: test_singleton.py# author: tom# official account: play test development from singleton import s as s1from singleton import s as slots Method One: implement def show_method_one () through import module: "": return: "" print (S1) print (S2) print (id (S1)) print (id (S2)) show_method_one () # Method Two: implement def singleton (cls) through decorator: # create a dictionary to hold the instance object of the class _ instance = {} def _ singleton (* args) * * kwargs): # first determine whether the class has an object if cls not in _ instance: _ instance[ CLS] = cls (* args, * * kwargs) # create an object and save it in the dictionary # return the instance object to return _ instance[ cls] return _ singleton@singletonclass Demo2 (object): a = 1 def _ init__ (self) ): self.x = xa1 = Demo2 (1) a2 = Demo2 (2) print (id (A1)) print (id (a2)) # Method Three: class Demo3 (object) through the use of classes: # static variable _ instance = None _ flag = False def _ new__ (cls, * args * * kwargs): if cls._instance is None: cls._instance = super (). _ _ new__ (cls) return cls._instance def _ _ init__ (self): if not Demo3._flag: Demo3._flag = Trueb1 = Demo3 () b2 = Demo3 () print (id (b1)) print (id (b2)) # Method Four: via _ _ new__ Method to realize class Demo4: def _ new__ (cls) * args, * * kwargs): if not hasattr (cls,'_ instance'): cls._instance = super (Demo4, cls). _ _ new__ (cls) return cls._instancec1 = Demo4 () c2 = Demo4 () print (id (C1)) print (id (c2))

Running result:

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