python单例模式原理与创建方法实例分析

# 实例化一个单例
class Singleton(object):
  __instance = None
  def __new__(cls, age, name):
    #如果类数字__instance没有或者没有赋值
    #那么就创建一个对象，并且赋值为这个对象的引用，保证下次调用这个方法时
    #能够知道之前已经创建过对象了，这样就保证了只有1个对象
    if not cls.__instance:
      cls.__instance = object.__new__(cls)
    return cls.__instance
a = Singleton(18, "xxx")
b = Singleton(8, "xxx")
print(id(a))
print(id(b))
a.age = 19 #给a指向的对象添加一个属性
print(b.age)#获取b指向的对象的age属性

# 实例化一个单例
class Singleton(object):
  __instance = None
  __first_init = False
  def __new__(cls, age, name):
    if not cls.__instance:
      cls.__instance = object.__new__(cls)
    return cls.__instance
  def __init__(self, age, name):
    if not self.__first_init:
      self.age = age
      self.name = name
      Singleton.__first_init = True
a = Singleton(18, "xxx")
b = Singleton(8, "xxx")
print(id(a))
print(id(b))
print(a.age)
print(b.age)
a.age = 19
print(b.age)