python中的單例模式的應用

標籤：單例   bsp   use   on()   def   屬性   pos   模組   字典   

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 共用屬性

建立執行個體時把所有執行個體的__dict__指向同一個字典,這樣它們具有相同的屬性和方法.

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 裝飾器版本

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

作為python的模組是天然的單例模式

# mysingleton.py
class My_Singleton(object):
    def foo(self):
        pass

my_singleton = My_Singleton()

# to use
from mysingleton import my_singleton

my_singleton.foo()

 

python中的單例模式的應用