python單例模式的五種實現方式

2021-10-09 21:33:44 字數 3158 閱讀 3242

1.__new__特殊方法實現

class

singleton

:def

__new__

(cls,

*args,

**kwargs):if

nothasattr

(cls,

'_instance'):

cls._instance =

super

(singleton, cls)

.__new__(cls)

return cls._instance

def__init__

(self, name)

: self.name = name

s1 = singleton(

'first'

)s2= singleton(

'last'

)print

(s1 == s2)

>>

true

print

(s1.name)

>> last

tips:new__方法無法避免觸發__init(),初始的成員變數會進行覆蓋

2.裝飾器實現

'''

'''def

singleton

(cls)

: _instance =

definner

(*args,

**kwargs)

:if cls not

in _instance:

_instance[cls]

= cls(

*args,

**kwargs)

return _instance[cls]

return inner

@singleton

class

test

:def

__init__

(self, name)

: self.name = name

t1 = test(

'first'

)t2 = test(

'last'

)print

(t1==t2)

>>

true

print

(t2.name)

>> first

3.類裝飾器實現

class

singleton

:def

__init__

(self, cls)

: self._cls = cls

self._instance =

def__call__

(self,

*args)

:if self._cls not

in self._instance:

self._instance[self._cls]

= self._cls(

*args)

return self._instance[self._cls]

@singleton

class

cls2

:def

__init__

(self, name)

: self.name = name

cls1 = cls2(

'first'

)cls2 = cls2(

'last'

)print(id

(cls1)

==id

(cls2)

)>>

true

print

(cls1.name)

>> first

4.元類實現

'''

'''class

singleton1

(type):

def__init__

(self,

*args,

**kwargs)

: self.__instance =

none

super

(singleton1, self)

.__init__(

*args,

**kwargs)

def__call__

(self,

*args,

**kwargs)

:if self.__instance is

none

: self.__instance =

super

(singleton1, self)

.__call__(

*args,

**kwargs)

return self.__instance

class

c(metaclass=singleton1)

:def

__init__

(self, name)

: self.name = name

c1 = c(

'first'

)c2 = c(

'last'

)print

(c1 == c2)

>>

true

print

(c2.name)

>> first

5.模組實現

python 的模組就是天然的單例模式,因為模組在第一次匯入時,會生成 .pyc 檔案,當第二次匯入時,就會直接載入 .pyc 檔案,而不會再次執行模組**。

#foo1.py

class

singleton

(object):

deffoo

(self)

:pass

singleton = singleton(

)#foo.py

from foo1 import singleton

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