單列模式 實現單列模式的五種方法

何為單列模式

不管例項化你建立多少的物件，我只給你們返回的總是哪乙個

class

mysql
(object):
_instance =
none
def__init__
(self, ip, port)
:        self.ip = ip
self.port = port
@classmethod
defsingleton
(cls):if
not cls._instance:
cls._instance = mysql(
'127.0.0.1'
,3306
)return cls._instance
if __name__ ==
'__main__'
:    obj1 = mysql.singleton(
)    obj2 = mysql.singleton(
)print
(obj1)
print
(obj2)

def

singleton
(cls)
:    _instance = cls(
'127.0.0.1'
,3306
)def
inner
(*args,
**kws)
:if args or kws:
return cls(
*args,
**kws)
return _instance
return inner
@singleton
class
mysql
(object):
def__init__
(self, ip, port)
:        self.ip = ip 
self.port = port
if __name__ ==
'__main__'
:    obj1 = mysql(
)    obj2 = mysql(
)print
(obj1)
print
(obj2)

class

mymetaclass
(type):
def__call__
(self,
*args,
**kws):if
nothasattr
(self,
'instance'):
self.instance =
super()
.__call__(
*args,
**kws)
return self.instance
class
mysql
(metaclass=mymetaclass)
:def
__init__
(self, ip, port)
:        self.ip = ip
self.port = port
if __name__ ==
'__main__'
:    obj1 = mysql(
'127.0.0.1'
,3306
)    obj2 = mysql(
'127.0.0.1'
,3308
)print
(obj1)
print
(obj2)

class

singleton
(object):
_instance =
none
def__new__
(cls,
*args,
**kws):if
not cls._instance:
cls._instance =
super()
.__new__(cls,
*args,
**kws)
return cls._instance
class
mysql
(singleton)
:def
__init__
(self)
:        self.ip =
'127.0.0.1'
self.port =
3306
if __name__ ==
'__main__'
:    obj1 = mysql(
)    obj2 = mysql(
)print
(obj1)
print
(obj2)

sing.py

class

mysql
(object):
def__init__
(self, ip, port)
:        self.ip = ip 
self.port = port
mysqlsingleton = mysql(
'127.0.0.1'
,2206
)

from sing import mysqlsingleton

單列模式幾種方法分析

方法一 懶漢式 懶漢式對於單執行緒而言，推薦使用，但是對於多執行緒，可能會出現 資料不同步，也可能會建立出好幾個物件，因此不建議使用 public class singlemodeltwo 執行緒不安全 return public static singlemodeltwo getinstance ...

六種單列模式

確保某乙個類只有乙個例項.1 餓漢式單列 public class singleone 構造方法私有 禁止建立 private singleone 2 懶漢式單列 public class singletwo 同步方法 每次呼叫都同步 消耗資源 public static synchronized ...

Python 裝飾器實現單列模式

使用裝飾器實現單列模式 defsingleton cls 用來存在例項的字典 singleton instance 判斷字典中是否例項 ifnot singleton instance.get cls.name 沒有則建立乙個例項，並存入字典中 singleton instance cls.name...