Python面向对象进阶2.html
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title: Python 面向对象进阶2
tags: Python
1 setitem getitem delitem
把 对象操作属性模拟字典格式
class Foo:
def __init__(self,name):
self.name=name
def __getitem__(self, item):
return self.__dict__[item] # getitem 通过return返回
def __setitem__(self, key, value):
self.__dict__[key]=value # 真正操作的是字典中的
def __delitem__(self,key):
# self.__dict__.pop[key] # 把字典中的删除
self.__dict__.pop(key) # pop是个函数
f=Foo('aaa') # 实例化
print(f['name']) # 这是getitem
f['age']=18 # setitem
print(f.__dict__)
打印结果：
{‘name’: ‘aaa’, ‘age’: 18}
f=Foo('aaa')
print(f['name'])
f['age']=18
del f['age'] # delitem
del f['name']
print(f.__dict__) # 通过查看对象的名称空间可
结果:
2 _slots_
slots是一个类变量，变量的值可以是列表、字典、字符串、可迭代对象,用的是类的名称空间，是共享的，对象没有自己的名称空间，省内存
class People:
__slots__=['x','y','z'] #设置相应的属性
p=People()
print(People.__dict__)
p.x=1
p.y=2
p.z=3
print(p.x,p.y,p.z)
# print(p.__dict__)
p1=People()
p1.x=11
p1.y=21
p1.z=31
print(p1.x,p1.y,p1.z)
结果：
1 2 3
11 21 31
slots应用：字典会占用大量内存，如果一个类的属性很少，但是有很多类，为了节省内存可以使用slots代替dict
3 __next和 ___iter__ 实现迭代器协议
可迭代对象内置iter方法，可迭代对象赋值就是一个迭代器，迭代器可以使用next方法
from collections import Iterator,Iterable
class Foo:
def __init__(self,start):
self.start=start
def __iter__(self):
return self
def __next__(self):
if self.start > 10:
raise StopIteration
n = self.start
self.start+=1
return n
f=Foo(5)
# print(next(f))
for i in f:
print(i)
4 _doc_
class Foo:
'这是描述信息'
pass
print(Foo.__doc__) # 打印的结果就是函数的注释信息
无法继承
class Foo:
'这是描述信息'
pass
class Bar(Foo):
pass
print(Bar.__dic__)
结果：
type object ‘Bar’ has no attribute ‘dic‘
5 _module 和 __class__
module 表示当前操作的对象在那个模块
class 表示当前操作的对象的类是什么
class Foo:
'这是描述信息'
pass
class Bar(Foo):
pass
# print(Bar.__dic__)
b=Bar()
print(b.__module__)
print(b.__class__)
print(Bar.__class__)
print(Foo.__class__)
结果：
main
class ‘main.Bar’>
class ‘type’>
class ‘type’>
6 _del_ 析构方法
但对象在内存中被释放时，自动触发_del_
class Foo(object):
"""docstring for Foo"""
def __del__(self):
print("zhi xing ")
f1 = Foo()
del f1
print('----')
文件操作
class Open:
def __init__(self,filepath,mode='r',encoding='utf-8'):
self.x = open(filepath,mode=mode,encoding=encoding)
# self.x = open(filepath,mode=mode,encoding=encoding)
self.filepath =filepath
self.mode=mode
self.encoding=encoding
def write(self,line):
self.x.write(line)
def __getattr__(self, item):
return getattr(self.x,item)
def __del__(self):
self.x.close()
f=Open('a.txt','w')
del f
7 __enter__ 和 __exit__上下文管理协议
上下文管理协议，即with语句，为了让一个对象兼容with语句必须在对象中声明enter 和iter