Python的四种单例模式实现方式

单例
├───file1.py
├───file2.py
├───readme
├───单例实现1_模块导入.py
└───模块导入实现单例测试.py

"""
模块导入实现单例模式步骤:
1. 在模块中定义类
2. 实例化类并返回
3. 在其他文件中导入实例对象使用, 每个文件导入的对象实际是同一个
"""
class Singleton:
    def __init__(self, name):
        self.name = name
    def do_something(self):
        pass
singleton = Singleton('模块单例')
# 在其他py文件中
# from my_singleton import singleton

from 单例实现1_模块导入 import singleton
print(singleton)

from 单例实现1_模块导入 import singleton
print(singleton)

import file1
import file2
print(file1.singleton is file2.singleton)

# -------------------函数装饰器---------------------------
def Singleton1(cls):
    instance = {}
    def _singleton_wrapper(*args, **kargs):
        if cls not in instance:
            instance[cls] = cls(*args, **kargs)
        return instance[cls]
    return _singleton_wrapper
# -------------------类装饰器---------------------------
class Singleton2:
    def __init__(self, cls):
        self.cls = cls
        self._instance = None
    def __call__(self, *args, **kwargs):
        if not self._instance:
            self._instance = self.cls(*args, **kwargs)
        return self._instance
# SingletonTest = Singleton1(SingletonTest) =_singleton_wrapper
# SingletonTest = Singleton2(SingletonTest) = Singleton2实例对象
@Singleton1
class SingletonTest(object):
    def __init__(self, name):
        print(">>> 初始化 <<<")
        self.name = name
s1 = SingletonTest('s1')
s2 = SingletonTest('s2')
print(s1, s2)
print(s1 is s2)
 

class Singleton(object):
    def __new__(cls, *args, **kwargs):
        if not hasattr(Singleton, "_instance"):
            Singleton._init_flag = True
            Singleton._instance = super().__new__(cls)
        return Singleton._instance
    def __init__(self, name):
        if not hasattr(Singleton, "_init"):
            Singleton._init = True
            print(">>> 初始化 <<<")
            self.name = name
s1 = Singleton('s1')
s2 = Singleton('s2')
print(s1, s2)
print(s1 is s2)

class Singleton(type):
    def __call__(cls, *args, **kwargs):
        if not hasattr(Singleton, "_instance"):
            # cls 是 Singleton 创建的类
            Singleton._instance = cls.__new__(cls, *args, **kwargs)
            cls.__init__(Singleton._instance, *args, **kwargs)
        return Singleton._instance
class SingletonTest(metaclass=Singleton):
    pass
class A(SingletonTest):
    def __init__(self, name):
        print(">>> 初始化 <<<")
        self.name = name
s1 = A('s1')
s2 = A('s2')
print(s1, s2)
print(s1 is s2)