python如何實作單一範例模式？以下帶給大家七種不同的方法：
一：staticmethod
程式碼如下：
class Singleton(object):
instance = None
def __init__(self):
raise SyntaxError('can not instance, please use get_instance')
def get_instance():
if Singleton.instance is None:
Singleton.instance = object.__new__(Singleton)
return Singleton.instance
a = Singleton.get_instance()
b = Singleton.get_instance()
print('a id=', id(a))
print('b id=', id(b))這個方法的重點是在__init__拋出異常，禁止透過類別來實例化，只能透過靜態get_instance函數來取得實例；因為不能透過類別來實例化，所以靜態get_instance函數中可以透過父類別object.__new__來實例化。
二：classmethod
和方法一類似，程式碼：
class Singleton(object):
instance = None
def __init__(self):
raise SyntaxError('can not instance, please use get_instance')
def get_instance(cls):
if Singleton.instance is None:
Singleton.instance = object.__new__(Singleton)
return Singleton.instance
a = Singleton.get_instance()
b = Singleton.get_instance()
print('a id=', id(a))
print('b id=', id(b))該方法的重點是在__init__拋出異常，禁止通過類別來實例化，只能透過靜態get_instance函數來取得實例；因為不能透過類別來實例化，所以靜態get_instance函數中可以透過父類別object.__new__來實例化。
三：類別屬性方法
與方法一類似， 程式碼：
class Singleton(object):
instance = None
def __init__(self):
raise SyntaxError('can not instance, please use get_instance')
def get_instance():
if Singleton.instance is None:
Singleton.instance = object.__new__(Singleton)
return Singleton.instance
a = Singleton.get_instance()
b = Singleton.get_instance()
print(id(a))
print(id(b))此方法的重點是在__init__拋出例外，禁止透過類別來實例化，只能透過靜態get_instance函數來取得實例；因為不能透過類別來實例化，所以靜態get_instance函數中可以透過父類別object.__new__來實例化。
四：__new__
常見的方法， 程式碼如下：
class Singleton(object):
instance = None
def __new__(cls, *args, **kw):
if not cls.instance:
# cls.instance = object.__new__(cls, *args)
cls.instance = super(Singleton, cls).__new__(cls, *args, **kw)
return cls.instance
a = Singleton()
b = Singleton()
print(id(a))
print(id(b))相關推薦：《Python影片教學》
五：裝飾器
程式碼如下：
def Singleton(cls):
instances = {}
def getinstance():
if cls not in instances:
instances[cls] = cls()
return instances[cls]
return getinstance
class MyClass:
pass
a = MyClass()
b = MyClass()
c = MyClass()
print(id(a))
print(id(b))
print(id(c))六：元類別
python2版：
class Singleton(type):
def __init__(cls, name, bases, dct):
super(Singleton, cls).__init__(name, bases, dct)
cls.instance = None
def __call__(cls, *args):
if cls.instance is None:
cls.instance = super(Singleton, cls).__call__(*args)
return cls.instance
class MyClass(object):
__metaclass__ = Singleton
a = MyClass()
b = MyClass()
c = MyClass()
print(id(a))
print(id(b))
print(id(c))
print(a is b)
print(a is c)或：
class Singleton(type):
def __new__(cls, name, bases, attrs):
attrs["_instance"] = None
return super(Singleton, cls).__new__(cls, name, bases, attrs)
def __call__(cls, *args, **kwargs):
if cls._instance is None:
cls._instance = super(Singleton, cls).__call__(*args, **kwargs)
return cls._instance
class Foo(object):
__metaclass__ = Singleton
x = Foo()
y = Foo()
print(id(x))
print(id(y))python3版：
class Singleton(type):
def __new__(cls, name, bases, attrs):
attrs['instance'] = None
return super(Singleton, cls).__new__(cls, name, bases, attrs)
def __call__(cls, *args, **kwargs):
if cls.instance is None:
cls.instance = super(Singleton, cls).__call__(*args, **kwargs)
return cls.instance
class Foo(metaclass=Singleton):
pass
x = Foo()
y = Foo()
print(id(x))
print(id(y))#七：名字覆蓋
程式碼如下：
class Singleton(object):
def foo(self):
print('foo')
def __call__(self):
return self
Singleton = Singleton()
Singleton.foo()
a = Singleton()
b = Singleton()
print(id(a))
print(id(b))以上是python如何實作單例模式的詳細內容。更多資訊請關注PHP中文網其他相關文章！
