可迭代对象，迭代器(对象)，生成器(对象)

迭代器

可迭代对象:可迭代对象实现了__iter__方法，该方法返回一个迭代器对象。

迭代器: 那么什么迭代器呢？它是一个带状态的对象，他能在你调用next()方法的时候返回容器中的下一个值，任何实现了__iter__和__next__（python2中实现next()）方法的对象都是迭代器，__iter__返回迭代器自身，__next__返回容器中的下一个值，如果容器中没有更多元素了，则抛出StopIteration异常。

a = ['aaa', 'bbb', 'ccc']
my_iterable = MyIterable(a)
res2 = iter(my_iterable)

while True:
    try:
        print(next(res2))
    except StopIteration as e:
        break

生成器

class Project(object):
    def __init__(self, start, end):
        self.start = start
        self.end = end

    def isPrimeNum(self, k): #  判断素数
        if k < 2:
            return False
        for i in range(2, k):
            if k % i == 0:
                return False
        return True

    def __iter__(self):
        for i in range(self.start, self.end):
            if self.isPrimeNum(i):
                yield i

###################################
res = Project(1,100)
print(iter(res))

正反序的自定义生成器

class MyFloatRange(object):
    def __init__(self, start, end, step):
        self.start = start
        self.end = end
        self.step = step

    def __iter__(self):
        for i in range(self.start, self.end):
            if self.start <= self.end:
                yield self.start
                self.start += self.step

    def __reversed__(self):
        for i in range(self.start, self.end):
            if self.start <= self.end:
                yield self.end
                self.end -= self.step


for i in MyFloatRange(1, 11, 2):
    print(i)

for i in reversed(MyFloatRange(1, 11, 2)):
    print(i)

如何对迭代器做切片操作

我们使用from itertools import islice

from itertools import islice

#对文件的每一行做切片操作
f = open("xxx.txt", "r")
res = islice(f, 3, 9)
循环res

如何在for循环中迭代多个对象(并行)

我们通过zip这个拉链函数

from random import randint
chin = [randint(50, 100) for _ in range(40)]
math = [randint(50, 100) for _ in range(40)]
eigh = [randint(50, 100) for _ in range(40)]

for x,y,z in zip(chin, math, eigh):
    print(x, y, z)

如何在for循环中迭代多个对象(串行)

我们通过from itertools import chain函数

from random import randint
from itertools import chain
chin = [randint(50, 100) for _ in range(5)]
math = [randint(50, 100) for _ in range(5)]
eigh = [randint(50, 100) for _ in range(5)]


for i in chain(chin, math, eigh):
    print(i)