7.29多态

a &＃61; 10
b &＃61; "10"
c &＃61; [10]print(type(a))
print(type(b))
print(type(c))
# type就是多态的体现

def add_num(a,b):if isinstance(a,int) and isinstance(b,int): # 判断传入的a是否为整型return a&＃43;b # 是就相加else:return Noneprint(add_num(20,10))
print(add_num(&＃39;a&＃39;,10))

class Person:def __str__(self):print(&＃39;run...&＃39;)return &＃39;字符串&＃39; # 必须返回字符串
p &＃61; Person()
str(p) # __str__会在对象被转换为字符串时执行
print(p) # 转换的结果就是这个函数的返回值

class Person:def __init__(self,name,age):self.name &＃61; nameself.age &＃61; agedef __str__(self):return "这是一个person对象 name:%s age:%s" % (self.name,self.age)p &＃61; Person("jack",20)
print(p) # 这是一个person对象 name:jack age:20
# 因为print会自动调用__str__&＃xff0c;把要打印的对象转为字符串再打印

class Person:def __init__(self,name,age):self.name &＃61; nameself.age &＃61; agedef __del__(self):print("del run")p &＃61; Person("jack",20)
del p # 可有可无&＃xff0c;不主动删除也会执行__del__&＃xff0c;因为程序结束时会自动删除对象

# 该类用于简化文件的读写操作
class FileTool:def __init__(self,path):self.file &＃61; open(path,"rt",encoding&＃61;"utf-8") # 执行完__del__后不会自动关闭self.a &＃61; 100 # 执行完__del__后会被自动删除def read(self):return self.file.read()# 在这里可以确定一个事,这个对象肯定不使用了&＃xff0c;所以可以放心的关闭问文件了def __del__(self):self.file.close()print(&＃39;文件已关闭&＃39;)tool &＃61; FileTool("a.txt")
print(tool.read())

class A:def __call__(self, *args, **kwargs):print("call run")print(args)print(kwargs)a &＃61; A()
a() # 对象加括号调用的时候会执行__call__
a(1,a&＃61;100) # 对象加括号调用的时候会执行__call__

import sys
class Person:__slots__ &＃61; ["name"] # 声明对象固定只有一个属性namedef __init__(self,name):self.name &＃61; namep &＃61; Person("francis")
print(sys.getsizeof(p))
# p.age &＃61; 20 # 报错&＃xff0c;无法再添加新的属性
# print(p.__dict__) # 报错&＃xff0c;也无法查看对象名称空间了

class A:def __getattr__(self, item):print("__getattr__")return 1def __setattr__(self, key, value):print("__setattr__")self.__dict__[key] &＃61; valuedef __delattr__(self, item):print("__delattr__")self.__dict__.pop(item)a &＃61; A()
a.name &＃61; "jack" # 设置属性时,执行__setattr__
print(a.age) # 访问不存在的属性时&＃xff0c;执行__getattr__&＃xff0c;并返回值
del a.name # 删除属性时,执行__delattr__

class A:def __getattr__(self, item):print("__getattr__")return 1def __getattribute__(self, item):print("__getattribute__")return super().__getattribute__(item)a &＃61; A()
print(a.name)

class A:def __getitem__(self, item):print("__getitem__")return self.__dict__[item]def __setitem__(self, key, value):print("__setitem__")self.__dict__[key] &＃61; valuedef __delitem__(self, key):del self.__dict__[key]print("__delitem__")a &＃61; A()
a["name"] &＃61; "jack" # 当你用中括号去设置属性时&＃xff0c;执行__setitem__
print(a["name"]) # 当你用中括号去获取属性时&＃xff0c;执行__getitem__
del a["name"] # 当你用中括号去删除属性时&＃xff0c;执行__delitem__

# 需求让一个对象支持 点语法来取值 也支持括号取值
class MyDict(dict,list):def __getattr__(self, key):return self.get(key)def __setattr__(self, key, value):self[key] &＃61; valuedef __delattr__(self, item):del self[item]a &＃61; MyDict()
a["name"] &＃61; "jack"
print(a["name"])
print(a.name)a.age &＃61; 20
print(a["age"])

class MyIter:# num传入&＃xff0c;用来指定迭代次数def __init__(self,num):self.num &＃61; num # 最大值&＃xff0c;用来指定最大迭代次数self.c &＃61; 0 # 初始值def __iter__(self):return selfdef __next__(self):self.c &＃43;&＃61; 1if self.c <&＃61; self.num:return "哈哈"else:raise StopIteration # 返回错误for i in MyIter(10):print(i)

class MyRange:def __init__(self,start,end,step&＃61;1):self.start &＃61; startself.end &＃61; endself.step &＃61; stepdef __iter__(self):return selfdef __next__(self):a &＃61; self.startself.start &＃43;&＃61; self.stepif a < self.end:return aelse:raise StopIterationfor i in MyRange(1,10,2):print(i)

class MyOpen(object):def __init__(self,path):self.path &＃61; pathdef __enter__(self):self.file &＃61; open(self.path)print("enter...")return self # enter函数应该返回对象自己def __exit__(self, exc_type, exc_val, exc_tb):print("exit...")self.file.close()return True# exit函数&＃xff0c;可以有返回值,是一个bool类型,用于表示异常是否被处理,仅在上下文中出现异常有用# 如果为True&＃xff0c;则意味着&＃xff0c;异常以及被处理了# 如果为False&＃xff0c;则意味着&＃xff0c;异常未被处理&＃xff0c;程序将中断报错

with MyOpen("a.txt") as m:print(m)print(m.file.read())"123"&＃43;1 # 错误信息&＃xff0c;被exit处理了