python 类的内置方法二

1.描述符

1.描述符就是将某种特殊类型的类的实例指派给另一个类的属性,特殊类型的类即实现下面某个或者全部的方法
- 访问属性 __get__(self,instance,owner)返回属性的值
- 分配属性时调用 __set__(self,instance,value)无返回值
- 删除时 __delete__(self,instance) 无返回值

class A:    def __get__(self,instance,owner):        print('__get__', instance, owner)    def __set__(self,instance,value):        print('__set__', instance, value)    def __delete__(self,instance):        print('__delete__', instance)class Test:    x = A()t = Test()t.x # __get__ <__main__.Test object at 0x000002B03BE9A550> <class '__main__.Test'>print(t) # <__main__.Test object at 0x000002785C3FA550>print(Test) # <class '__main__.Test'>t.x = 20 # __set__ <__main__.Test object at 0x000002785C3FA550> 20del t.x # __delete__ <__main__.Test object at 0x0000024B0EC0A550>

2.描述符与property(property()函数就是描述符类)

class MyProperty:    def __init__(self,fget = None,fset = None,fdel = None):        self.fget = fget        self.fset = fset        self.fdel = fdel    def __get__(self,instance,owner):        return self.fget(instance)    def __set__(self,instance,value):        self.fset(instance,value)    def __delete__(self,instance):        self.fdel(instance)class A:    def __init__(self):        self.num = None    def getNum(self):        return self.num    def setNum(self, value):        self.num = value    def delNum(self):        del self.num    x = MyProperty(getNum,setNum,delNum) # 与property类似a = A()a.x = 20print(a.x) # 20print(a.num) # 20del a.num

3.列表生成式

可用range(1,n)生成[1,2,3….n]的列表

>>> list(x * x for x in range(1,11))[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

4.迭代

通过for循环称为迭代

a = {"语文":90,"数学":100,"python":100}for k,v in a.items():    print("%s-->%d" %(k, v))--------------语文-->90数学-->100python-->100

1.Iterable判断对象是否可迭代对象

from collections import Iterablea = {"语文":90,"数学":100,"python":100}flag = isinstance(a,Iterable)print("对象是否可迭代：" , flag) # True

5.生成器generator

可以通过列表生成式生成列表，也可通过生成器generator一边循环一边计算的机制生成列表

a = (x * x for x in range(1,11))print(a) # a为生成器print(next(a))print(next(a))next(a)没有下一个元素会抛出StopIteration异常------------------b = (x * x for x in range(1,11))for item in b:    print(item)

1.yield语句

遇到yield语句返回，再次执行时从上次返回的yield语句处继续执行
方法中出现yield则说明这个函数不是普通函数而是一个generator
yield 返回后面的值相当于return

def fun():    print('one print')    yield 111    print('two print')    yield 222    print('three print')    yield 333f = fun()for item in f:    print('item的值为%d' % item)-----------one printitem的值为111 two printitem的值为222three printitem的值为333