方法一
实现__new__方法
并在将一个类的实例绑定到类变量_instance上,
如果cls._instance为None说明该类还没有实例化过,实例化该类,并返回
如果cls._instance不为None,直接返回cls._instance
class Singleton(object):
def __new__(cls, *args, **kwargs):
if not hasattr(cls, '_instance'):
cls._instance = super(Singleton, cls).__new__(cls, *args, **kwargs)
return cls._instance
class A(Singleton):
def __init__(self, s, v):
self.s = s
self.v = v
a = A(1, 5)
b = A(2, 4)
print id(a), a.s
print id(b), b.v
"""
import borg
其他文件调用borg的A类的实例即可调用其属性
eg:
print borg.a.s
print borg.b.v
"""
方法二
共享模式;所谓单例就是所有引用(实例、对象)拥有相同的状态(属性)和行为(方法)
同一个类的所有实例天然拥有相同的行为(方法),
只需要保证同一个类的所有实例具有相同的状态(属性)即可
所有实例共享属性的最简单最直接的方法就是__dict__属性指向(引用)同一个字典(dict)
Tips: 这是一种特殊的单例方式,多个实例对象共享属性a singleton with shared-state among instances
class Borg:
__shared_state = {}
def __init__(self):
self.__dict__ = self.__shared_state
self.state = 'Init'
def __str__(self):
return self.state
class YourBorg(Borg):
pass
if __name__ == '__main__':
rm1 = Borg()
rm2 = Borg()
rm1.state = 'Idle'
rm2.state = 'Running'
print('rm1: {0}'.format(rm1))
print('rm2: {0}'.format(rm2))
rm2.state = 'Zombie'
print('rm1: {0}'.format(rm1))
print('rm2: {0}'.format(rm2))
print('rm1 id: {0}'.format(id(rm1)))
print('rm2 id: {0}'.format(id(rm2)))
rm3 = YourBorg()
print('rm1: {0}'.format(rm1))
print('rm2: {0}'.format(rm2))
print('rm3: {0}'.format(rm3))
方法三
本质上是方法1的升级（或者说高级版)
使用__metaclass__（元类）的高级python用法
class Basic(type):
def __init__(cls, *args, **kwargs):
super(Basic, cls).__init__(*args, **kwargs)
def __new__(cls, *args, **kwargs):
return super(Basic, cls).__new__(cls, *args, **kwargs)
class Foo:
__metaclass__ = Basic
Foo.color = 'red'
Foo.borderWidth = 1
class rect:
def __init__(self, color, borderWidth):
self.color = color
self.borderWidth = borderWidth
if __name__ == '__main__':
Foo.color = 'blue'
a = rect(Foo.color, Foo.borderWidth)
print a.__dict__
"""
from borg import Foo
其他文件调用Foo类的属性即可
eg:
print Foo.color
print Foo.borderWidth
"""
方法四
使用装饰器(decorator),
这是一种更pythonic,更elegant的方法,
单例类本身根本不知道自己是单例的,因为他本身(自己的代码)并不是单例的
def singleton(cls, *args, **kw):
instances = {}
def _singleton():
if cls not in instances:
instances[cls] = cls(*args, **kw)
return instances[cls]
return _singleton
@singleton
class MyClass(object):
a = 1
def __init__(self, x=0):
self.x = x
one = MyClass()
two = MyClass()
two.a = 3
print one.a
# 3
print id(one)
# 29660784
print id(two)
# 29660784
print one == two
# True
print one is two
# True
one.x = 1
print one.x
# 1
print two.x
# 1