使用全局变量
我个人比较喜欢的方式,简单高效。
class Application:
pass
APP = Application()
装饰器(使用特定方法来获取对象实例)
import threading
class singleton:
_instance_lock = threading.Lock()
def __init__(self, decorated):
self._decorated = decorated
def instance(self):
if not hasattr(self, '_instance'):
with singleton._instance_lock:
if not hasattr(self, '_instance'):
self._instance = self._decorated()
return self._instance
def __call__(self):
raise TypeError('Singletons must be accessed through `instance()`.')
def __instancecheck__(self, inst):
return isinstance(inst, self._decorated)
def __getattr__(self, name):
if name == '_instance':
raise AttributeError("'singleton' object has no attribute '_instance'")
return getattr(self.instance(), name)
@singleton
class Application:
pass
Application.instance()
装饰器
def singleton(cls):
_instances = {}
def _inner(*args, **kargs):
if cls not in _instances:
_instances[cls] = cls(*args, **kargs)
return _instances[cls]
return _inner
元类
class Application:
_instance_lock = threading.Lock()
def __new__(cls, *args, **kwargs):
if not hasattr(cls, "_instance"):
with cls._instance_lock:
if not hasattr(cls, "_instance"):
cls._instance = object.__new__(cls)
return cls._instance
改成通用方式:
import threading
class SingletonMeta(type):
_instances = {}
_instance_lock = threading.Lock()
def __call__(cls, *args, **kwargs):
if cls not in cls._instances:
with cls._instance_lock:
if cls not in cls._instances:
instance = super().__call__(*args, **kwargs)
cls._instances[cls] = instance
return cls._instances[cls]
class Application(metaclass=SingletonMeta):
pass