#python中单例模式
#1.使用__new__
class Singleton:
def __new__(cls,*args,**kwargs):
if not hasattr(cls,'_instance'):
cls._instance=super().__new__(cls)
return cls._instance
s0=Singleton()
s1=Singleton()
print(id(s0))
print(id(s1))
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#hasattr(object,name)函数用于判断是否包含对应的属性
#参数: object------对象 name------字符串,属性名
#返回值: 如果对象有该属性返回True,否则返回False
class People:
country="china"
def __init__(self,name):
self.name=name
def people_info(self):
print("%s is xxx"%(self.name))
obj=People('aaa')
print(obj.name)
print(hasattr(People,'country'))
print(hasattr(obj,'name'))
print(hasattr(People,'name'))
print(hasattr(People,'people_info'))
print(hasattr(obj,'people_info'))
print(People.__dict__)
print(obj.__dict__)
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#2.使用装饰器
from functools import wraps
def singlenton(cls):
instances={}
@wraps(cls)
def getinstance(*args,**kwargs):
if cls not in instances:
instances[cls]=cls(*args,**kwargs)
return instances
return getinstance
@singlenton
class Bar:
pass
b0=Bar()
b1=Bar()
print(id(b0))
print(id(b1))
装饰器的用法(小应用)
def outer(func): def inner(): print("before func") ret=func() return ret+1 return inner #返回inner函数
@outer #解释器执行 foo=outer(foo) def foo(): return 1
print(foo) foo()
这个过程中执行了下面几步
1.函数 foo 作为 装饰器 outer 的参数被传入 2.函数 inner 对 func 进行调用,然后装饰器 outer 返回 inner 3.原来的函数名 foo 关联到 inner,如上面的foo 所示,调用 foo时间上是在调用 inner
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#装饰器的应用小例子
#将对象作为函数的参数,去判断对象参数
def wrapper(func):
def checker(a,b):
if a.x<0 or a.y <0:
a=Coordinate(a.x if a.x>0 else 0,a.y if a.y>0 else 0)
if b.x<0 or b.y<0:
b=Coordinate(b.x if b.x>0 else 0,b.y if b.y>0 else 0)
ret=func(a,b)
if ret.x<0 or ret.y<0:
ret = Coordinate(ret.x if ret.x>0 else 0,re.y if ret.y>0 else 0)
return ret
return checker
class Coordinate(object):
def __init__(self,x,y):
self.x=x
self.y=y
def __repr__(self):
return "Coord:"+str(self.__dict__)
@wrapper
def add(a,b):
return Coordinate(a.x+b.x,a.y+b.y)
@wrapper
def sub(a,b):
return Coordinate(a.x-b.x,a.y-b.y