单例模式
一、什么是单例模式
- 单例模式：基于某种方法实例化多次得到实例是同一个
二、为什么用单例模式
- 当实例化多次得到的对象中存放的属性都一样的情况，应该将多个对象指向同一个内存，即同一个实例
三、单例模式
3.1 静态方法实现
"""
当用户输入端口和地址，实例化产生新对象
当用户输入端口和地址，每次拿到的对象，是同一个
"""
class Single:
_single_model = None
def __init__(self, port, host):
self.port = port
self.host = host
@classmethod
def single_cls(cls):
import settings
if not cls._single_model:
cls._single_model = cls(settings.PORT, settings.HOST)
return cls._single_model
# 拿到的对象会是同一个
s = Single.single_cls()
s2 = Single.single_cls()
print(s)
print(s2)
<__main__.Single object at 0x00000210F3F7CD68>
<__main__.Single object at 0x00000210F3F7CD68>
3.2通过装饰器实现
"""
第二种方法，通过装饰器实现
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
"""
def get_siggle(cls):
import settings
siggle = cls(settings.PORT, settings.HOST)
def wrapper(*args, **kwargs):
if len(args) != 0 or len(kwargs) != 0:
res = cls(*args, **kwargs)
return res
else:
return siggle
return wrapper
@get_siggle
class Single:
def __init__(self, port, host):
self.port = port
self.host = host
s1 = Single()
s2 = Single()
print(s1)
print(s2)
"""
"""
<__main__.Single object at 0x000001A4DE282198>
<__main__Single object at 0x000001A4DE282198>
3.3 通过元类
"""
第三种方法通过元类
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
"""
class Mymeta(type):
def __init__(self, name, base, dic):
# self 是singie类
import settings
# 把实例化好的对象，放到了类的名称空间
self._singie = self(settings.PORT, settings.HOST)
def __call__(self, *args, **kwargs):
if len(args) != 0 or len(kwargs) != 0:
obj =self.__new__(self)
obj.__init__(*args, **kwargs)
return obj
else:
return self._singie
class Singie(metaclass=Mymeta):
def __init__(self, port, host):
self.port = port
self.host = host
s1 = Singie()
s2 = Singie()
print(s1, "dddd")
print(s2,"dfd")
<__main__.Singie object at 0x000001324C1247F0>
<__main__.Singie object at 0x000001324C1247F0>
3.4通过模块实现
# settings.py
PORT = '3306'
HOST = '127.0.0.0'
# singie.pyt
import settings
class Singies():
def __init__(self, port, host):
self.port = port
self.host = host
s1 = Singies(settings.PORT, settings.HOST)
# 通过模块导入（python的模块是天然的单例）
def test():
from singie import s1
print(s1.port)
print(s1)
def test2():
from singie import s1 as s2
print(s2)
test()
test2()
from singie import Singies
s3 = Singies('3306', '198.2.2.1')
print(s3)
<singie.Singies object at 0x000001324C1249E8>
<singie.Singies object at 0x000001324C1249E8>
<singie.Singies object at 0x000001324C124860>
四、总结
单例模式，只要把握类名()创建对象是唯一一个就行