9.4 之单例模式
单例模式定义：整个过程中只有一个实例,所有生成的实例都指向同一块内存空间
第一种：（类的绑定方法）
PORT = 3306
HOST = '127.0.0.1'
class Sql:
instance = None
def __init__(self,port,host):
self.port = port
self.host = host
@classmethod
def get_sigo(cls):
if not cls.instance:
cls.flag = cls(PORT,HOST)
return cls.instance
#每次调用get_sigoleton 拿到的对象都是同一个
s1=Sql.get_si()
s2=Sql.get_si()
s3=Sql.get_si()
s4=Sql('33306','192.168.1.1')
print(s1)
print(s2)
print(s3)
print(s4)
'''
<__main__.Sql object at 0x02DF4030>
<__main__.Sql object at 0x02DF4030>
<__main__.Sql object at 0x02DF4030>
<__main__.Sql object at 0x02DF4190>
'''
第二种：（装饰器）
#当用户输入端口和地址,实例化产生新对象
#当用户不输入端口和地址,每次拿到的对象,都是同一个
PORT = 3306
HOST = '127.0.0.1'
def get_sigo(func):
instance = None
def wrapper(*args,**kwargs):
if len(args) != 0 or len(kwargs) != 0:
#表示传了参数，生成新对象
res = func(*args,**kwargs)
return res
else:
nonlocal instance
if not instance:
instance = func(PORT,HOST)
return instance
return wrapper
@get_sigo
class Sql:
def __init__(self,port,host):
self.port = port
self.host = host
s1=Sql()
s2=Sql()
s3=Sql('33306','192.168.1.1')
s4=Sql('33306','192.168.1.1')
print(s1)
print(s2)
print(s3)
print(s4)
'''
<__main__.Sql object at 0x036A41B0>
<__main__.Sql object at 0x036A41B0>
<__main__.Sql object at 0x036A41D0>
<__main__.Sql object at 0x036A41F0>
'''
第三种：（元类）
PORT = 3306
HOST = '127.0.0.1'
class Mymeta(type):
def __init__(self,name,bases,dic):
# 把实例化好的对象，放到类的名称空间
self.instance = self(PORT,HOST)
def __call__(self,*args,**kwargs):
if len(args) != 0 or len(kwargs) != 0:
obj = object.__new__(self)
obj.__init__(*args,**kwargs)
return obj
else:
return self.instance
class Sql(metaclass = Mymeta):
def __init__(self,port,host):
self.port=port
self.host=host
print(Sql.__dict__)
s1=Sql()
s2=Sql()
s3=Sql('33306','192.168.1.1')
print(s1)
print(s2)
print(s3)
'''
<__main__.Sql object at 0x034740D0>
<__main__.Sql object at 0x034740D0>
<__main__.Sql object at 0x03474050>
'''
第四种：（模块导入）
# sigo 文件
# ************************************
PORT = 3306
HOST = '127.0.0.1'
class Sql():
def __init__(self,port,host):
self.port=port
self.host=host
s1=Sql(PORT,HOST)
# ************************************
def test():
from sigo import s1
print(s1)
def test2():
from sigo import s1 as s2
print(s2)
test()
test2()
from sigo import s1
from sigo import Sql
s2=Sql(3306,'192.168.1.1')
print(s1)
print(s2)
'''
<sigonleton.Sql object at 0x03A46AB0>
<sigonleton.Sql object at 0x03A46AB0>
<sigonleton.Sql object at 0x03A46AB0>
<sigonleton.Sql object at 0x03A22E30>
'''
转载于:https://www.cnblogs.com/dadazunzhe/p/11461768.html
