1 使用__new__方法
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
2 共享属性
创建实例时把所有实例的__dict__指向同一个字典,这样它们具有相同的属性和方法.
class Borg(object):
_state = {}
def __new__(cls, *args, **kw):
ob = super(Borg, cls).__new__(cls, *args, **kw)
ob.__dict__ = cls._state
return ob
class MyClass2(Borg):
a = 1
3 装饰器版本
def singleton(cls, *args, **kw):
instances = {}
def getinstance():
if cls not in instances:
instances[cls] = cls(*args, **kw)
return instances[cls]
return getinstance
@singleton
class MyClass:
...
4:import版本
作为python的模块是天然的单例模式
# mysingleton.py
class My_Singleton(object):
def foo(self):
pass
my_singleton = My_Singleton()
# to use
from mysingleton import my_singleton
my_singleton.foo()