一、 isinstance(obj,cls)和issubclass(sub,super)
isinstance(obj,cls)检查obj是否是类 cls 的对象
class Foo:
pass
obj=Foo()
print(isinstance(obj,Foo))
打印结果为
True
issubclass(sub, super)检查sub类是否是 super 类的派生类
class Foo(object):
pass
class Bar(Foo):
pass
print(issubclass(Bar, Foo))
d打印结果为
True
二、反射
1、概念：主要是指程序可以访问、检测和修改它本身状态或行为的一种能力（自省）
2、四个实现反射的函数：都是通过字符串的形式
(1)hasattr(object,name):判断object中有没有一个name字符串对应的方法或属性
def getattr(object, name, default=None): # known special case of getattr
"""
getattr(object, name[, default]) -> value
Get a named attribute from an object; getattr(x, 'y') is equivalent to x.y.
When a default argument is given, it is returned when the attribute doesn't
exist; without it, an exception is raised in that case.
"""
pass
(2)getattr(object,name):查看类object中的name字符串对应的值
def getattr(object, name, default=None): # known special case of getattr
"""
getattr(object, name[, default]) -> value
Get a named attribute from an object; getattr(x, 'y') is equivalent to x.y.
When a default argument is given, it is returned when the attribute doesn't
exist; without it, an exception is raised in that case.
"""
pass
（3）setattr（object,name,value）:将object中name字符串的值设置为value
def setattr(x, y, v): # real signature unknown; restored from __doc__
"""
Sets the named attribute on the given object to the specified value.
setattr(x, 'y', v) is equivalent to ``x.y = v''
"""
pass
（4）delattr(object,name):删除object类中的name字符串属性
def delattr(x, y): # real signature unknown; restored from __doc__
"""
Deletes the named attribute from the given object.
delattr(x, 'y') is equivalent to ``del x.y''
"""
pass
（5）综合示例
class People:
country='China'
def __init__(self,name):
self.name=name
def walk(self):
print('%s is walking' %self.name)
p=People('egon')
print('name' in p.__dict__)
print(hasattr(p,'name')) #hasattr查看是p实例内是否有name属性
print(hasattr(p,'country'))
print(hasattr(People,'__init__'))
print(getattr(p,'walk')) #getattr查看p对象内walk的属性值
res=getattr(p,'country') #getattr获取属性
print(res)
getattr(p,'xxxxxxxxx','这个属性不存在') #可以指定返回值，如果要找的属性不存在，会返回指定的字符串
setattr(p,'country','123') #setattr修改
print(getattr(p,'country'))
delattr(p,'country') #delattr删除p对象内的country
print(hasattr(p,'country')) #查看p对象内还有没有country
打印结果如下
True
True
True
True
<bound method People.walk of <__main__.People object at 0x00000000010847F0>>
China
123
True
三、内置函数attr(setattr,getattr,delattr)
#setattr:设置属性
# getattr：查找属性，只在对象不存在的情况下才触发
# delattr：删除属性
#这些内置方法只是确定了class的调用方法，具体的操作需要def 内部的代码
class Foo:
def __init__(self,name):
self.name=name
def __setattr__(self, key, value): #设置
print('-----setattr---key:%s,value:%s'%(key,value))
print(type(key))
print(type(value))
self.__dict__[key]=value
def __delattr__(self, item): #删除
print('delattr:%s' %item)
del self.__dict__[item]
def __getattr__(self, item): #属性不存在的情况下才会触发
print('getattr-->%s %s' %(item,type(item)))
四、综合示例：定制自己的数据类型（继承）
#创建列表，往列表内插入元素，每个元素都必须是int
class List(list): #创建List类，继承list
def append(self, p_object): #append函数
print('------>',p_object)
if not isinstance(p_object,int): #如果p_object不是int，返回类型错误
raise TypeError('必须是整型')
super().append(p_object) #如果是int，调用父类（list）的append方法将值插入列表
def insert(self,index,p_object): #定义一个insert函数
if not isinstance(p_object,int):
raise TypeError('必须是整型')
super().insert(index,p_object)
l=List([1,2,3])
print(l)
l.append(4)
print(l)
l.insert(4,5)
print(l)
五、综合示例：授权的方式定制文件的增删改查
import time
class Open:
def __init__(self,filepath,mode='r',encoding='utf8'):
self.filepath=filepath
self.mode=mode
self.encoding=encoding
self.x=open(filepath,mode=mode,encoding=encoding)
def write(self,line):
t=time.strftime('%Y-%m-%d %x')
self.x.write('%s %s' %(t,line))
def __getattr__(self, item):
return getattr(self.x,item)
f=Open('b.txt','w')
f.write('1111111\n')
f.write('2222222\n')
f.write('3333333\n')
f.write('3333333\n')
f.close()
f=Open('b.txt','r+')
# f.seek(0)
res=f.read()
print(res)
