Python3.x基础学习-迭代器用法

迭代器

拥有__iter__方法和__next__方法的对象就是迭代器
1.迭代 迭代是访问集合元素的一种方式，可以将某个数据集内的数据“一个挨着一个的取出来”，就叫做迭代
2.可迭代协议 协议就是互相规定好。可迭代协议的定义非常简单，就是内部实现了__iter__方法。
3.迭代器协议：必须拥有__iter__方法和__next__方法。

for i in 'abc':
    print(i)

for i in [1,2,3]:
    print(i)

for i in (1,2,3):
    print(i)

for i in {'a':1,'b':3}:
    print(i)

# for i in 123:
#     print(i)

from collections import Iterable

print(isinstance('abc',Iterable))
print(isinstance(123,Iterable))
print(isinstance([1,3,4],Iterable))
print(isinstance({1,3,4},Iterable))
print(isinstance({'a':123,'b':321},Iterable))

# True
# False
# True
# True
# True

#自定义一个能容纳数据的类，测试可迭代性

from collections import Iterable

class Students:
    def __init__(self):
        self.names = []
    def add(self,name):
        self.names.append(name)
    def __iter__(self):  #只要内部有__iter__方法，就是可迭代对象
        pass
stu = Students()
stu.add('johnson')
print(isinstance(stu,Iterable))
# True

class Students:
    def __init__(self):
        self.names = []
        self.index = 0

    def add(self,name):
        self.names.append(name)

    def __iter__(self):
        return self

    def __next__(self):
        if self.index < len(self.names):
            name = self.names[self.index]
            self.index+=1
            return name
        else:
            raise StopIteration

stu = Students()  #实例化对象
stu.add('johnson')
stu.add('may')
for i in stu:
    print(i)
    
# johnson
# may

iter1 = iter(stu)
print(next(iter1))

#StopIteration

#使用迭代器实现斐波那契 0,1,1,2,3,5

class Fib:
    def __init__(self,n):
        self.n = n
        self.index=0
        self.a=0
        self.b =1

    def __iter__(self):
        return self

    def __next__(self):

        if self.index<=self.n:
            self.a,self.b = self.b,self.b+self.a
            self.index+=1
            return self.a

        else:
            raise StopIteration


fib = Fib(10)

iter2 = iter(fib)
print(next(iter2))
print(next(iter2))
print(next(iter2))
print(next(iter2))

# 1
# 1
# 2
# 3