python 实现单例模式的5种方法

# 全局变量
ip = '192.168.13.98'
port = '3306'
class MySQL:
  __instance = None
 
  def __init__(self, ip, port):
    self.ip = ip
    self.port = port
 
  @classmethod
  def instance(cls, *args, **kwargs):
    if args or kwargs:
      cls.__instance = cls(*args, **kwargs)
    return cls.__instance
 
 
obj1 = MySQL.instance(ip, port)
obj2 = MySQL.instance()
obj3 = MySQL.instance()
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)

def singlegon(cls):
  _instance = cls(ip, port)
 
  def wrapper(*args, **kwargs):
    if args or kwargs:
      return cls(*args, **kwargs)
    return _instance
 
  return wrapper
 
 
@singlegon
class MySQL1:
  def __init__(self, ip, port):
    self.ip = ip
    self.port = port
 
 
obj1 = MySQL1()
obj2 = MySQL1()
obj3 = MySQL1('1.1.1.3', 8080)
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)
　　

class Mymetaclass(type):
  def __init__(self, class_name, class_bases, class_dic):
    super().__init__(class_name, class_bases, class_dic)
    self.__instance = self(ip, port)
 
  def __call__(self, *args, **kwargs):
    if args or kwargs:
      obj = self.__new__(self)
      self.__init__(obj, *args, **kwargs)
      self.__instance = obj
    return self.__instance
 
 
class MySQL2(metaclass=Mymetaclass):
  def __init__(self, ip, port):
    self.ip = ip
    self.port = port
 
 
obj1 = MySQL2()
obj2 = MySQL2()
obj3 = MySQL2('1.1.1.3', 80)
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)

# instance.py
 
class MySQL:
  def __init__(self, ip, port):
    self.ip = ip
    self.port = port
 
 
ip = '192.168.13.98'
port = 3306
instance = MySQL(ip, port)
 
 
# 测试代码
import os, sys
 
sys.path.append(os.path.dirname(os.path.dirname(__file__)))
from test import instance
 
 
obj1 = instance.instance
obj2 = instance.instance
obj3 = instance.MySQL('1.1.1.3', 80)
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)

class MySQL3(object):
  __instance = None
  __first_init = True
 
  def __init__(self, ip, port):
    if self.__first_init:
      self.ip = ip
      self.port = port
      self.__first_init = False
 
  def __new__(cls, *args, **kwargs):
    if not cls.__instance:
      cls.__instance = object.__new__(cls)
    return cls.__instance
 
obj1 = MySQL3(ip, port)
obj2 = MySQL3(ip, port)
obj3 = MySQL3('1.1.1.3', 80)
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)