1 鸭子类型和多态
维基百科：当看到一只鸟走起来像鸭子，游泳起来像鸭子，叫起来也像鸭子，那么这只鸟就可以被称为鸭子
class Cat(object):
def say(self):
print('i am a cat')
class Dog(object):
def say(self):
print('i am a dog')
class Duck(object):
def say(self):
print('i am a duck')
#animal=Cat
#animal().say()
#只需要共同实现say()方法就可以了
animal_list=[Cat,Dog.Duck]
for animal in animal_list:
animal().say()
a = ["today1","today2"]
b = ["today2","today"]
name_tuple = ["bobay3","bobay4"]
name_set = set()
name_set.add("today5")
name_set.add("today6")
a.extend(b)
print(a)
2 抽象基类(abc模块) - 1
抽象基类（abstract base class）类似java中的接口
3 抽象基类(abc模块) - 2
class Company(object):
def __init__(self,employee_list):
self.employee=employee_list
def __len__(self):
return len(self.employee)
com=Company("today1","today2")
print(hasattr(com,"__len__"))
print(len(com))
#我们希望在某些情况之下判定某个对象的类型
from collections.abc import Sized
is instance(com,Sized)
#我们需要强制某个子类需要实现某些方法
#实现了一个web框架，集成cache(redis,cache,memerychache)
#需要设计一个抽象基类，指定子类必须实现某些方法
#如何去模拟一个抽象基类
import abc
class CacheBase(metac)
class CacheBase():
def get(self,key)
raise NotImplementedError
def set(self,key,value):
raise NotImplementedError
class RedisCache(CacheBase):
pass
from collections.abc import *
class CacheBase(metaclass=abc.ABCMeta):
@abc.abstractmethord
def get(self,key):
pass
@abc.abstractmethord
def set(self,key,value):
rasie
class RedisCache(CacheBase):
pass
redis_cache=RedisCache()
4 isinstance和type的区别
class A:
pass
class B(A):
pass
print(isinstance(b,B))
print(isinstance(b,A))
print(type(b) is A )
print(type(b) is B)
#尽量使用isinstance去判断类型，type主要是判断两个的值是否相等
5 类变量和实例变量
class A:
aa=1
#self是类的实例
def __init__(self,x,y):
self.x=x
self.y=y
a=A(2,3)
print(a.x,a.y,a.aa)
A.aa=11
a.aa=100
print(a.x,a.y,a.aa)
print(a.aa)
b=A(3,5)
print(b.aa)
#先查找实例变量，然后查找类变量
####6 类和实例属性的查找顺序—mro查找
class A:
name="A"
def __init__(self):
self.name="obj"
a=A()
print(a.name)
#新式类
class D:
pass
class C(D):
pass
class B(D):
pass
class A(B,C):
pass
print(A.__mro__)
7 类方法、静态方法和实例方法
class Date:
#构造函数
def __init__(self,,year,month,day):
self.year=year
seif.month=month
self.day=day
def __str__(self):
return "{year}/{month}/{day}".format(year=self.year,month=self.month,day=self.day)
if __name++=="__main__":
new_day=Date(2019,9,02)
print(new_day)
#2019-09-02
data_str ="2019-9-02"
year,month,day=tuple(data_str,split("-"))
new_day=Date(int(year),int(month),int(day))
print(new_day)
####
8 数据封装和私有属性
class User:
def __init__(self,birthday):
self.birthday = birthday
def get_age(self):
#返回年龄
return 2018-self.birthday.year
if __name__=="__main__":
User=User(Date(1990,2,1))
print(User.get_age())
print(User.birthday)
print(User.get_age( ) )
9 python对象的自省机制
#自省是通过一定的机制查询到对象的内部结构
class Person:
name="user"
class Student(Person):
def __init__(self,school_name):
self.school_name=school_name
if __name__=="__main__":
user=Student("慕课网")
#通过__dict__查询属性
print(user.__dict__)
user.__dict__["school_addr"] ="北京市"
print(user.school_addr)
print(Person.__dict__)
print(user.name)
a=[1,2]
print(dir(a))
10 super真的是调用父类吗？
class A:
def __init__(self):
print("A")
class B(A):
def __init__(self):
print("B")
super().__init__()
from threading import Thread
class MyThread(Thread):
def __init__(self,name,user):
self.user = user
self.name = name
#既然重写了B的构造函数，为什么还要去调用super
#super到底执行顺序是什么样的？
if __name__=="__main__":
b=B()
class A:
def __init__(self):
print("A")
class B(A):
def __init__(self):
print("B")
super().__init__()
class C(A):
def __init__(self):
print ("C")
super().__init__()
class D(B,C):
def __init__(self):
print ("D")
super(D，self).__init__()
if __name__=="__main__":
print(D.__mro__):
d=D()
11 mixin继承案例-django rest framework
#mixin模式特点
1.Mixin类功能单一
2.不和基类关联，可以和任意基类组合，基类可以不和Mixin关联就能初始化成功
3.在Mixin中不要使用super这种用法
class GoodsListViewSet(CacheResponseMixin,Mixins.ListModelMixin,mixins.RetrieveModelMixin
12 python中的with语句
#try,except,finally
try:
print ("code started")
raise KeyError
except KeyError as e:
print ("Key error")
except IndexError as e:
else:
print("other error")
finally:
f_read.close()
#try,except,finally
def exe_try():
try:
print ("code started")
raise KeyError
return 1
except KeyError as e:
print ("key error")
return 2
else:
print("other error")
return 3
finally:
print("finally")
return 4
if __name__=="__main__":
result=exe_try
print(result)
#上下文管理器协议
class Sample():
def __enter__(self):
#获取资源
print("enter")
return self
def __exit__(self,exc_type,exc_val,exc_tb):
#(释放资源)
print("exit")
def do_something(self):
print ("do something")
with Sample() as sample:
sample.do_something()
13 contextlib简化上下文管理器
import contextlib
@contextlib.contextmanager
def file_open(file_name):
print("file open")
yield {}
print ("file end")
with file_open("today.txt") as f_opened:
print ("file processing")
14 本章小结
python中一切皆对象，鸭子类型和多态，鸭子类型实际上没有接口，遵循了python中的一些协议将魔法函数进行组合，抽象基类，mixin,类变量和对象变量，对象自省，super查找顺序，with语句，contextlib上下文管理器.
