迭代

       迭代：通过 for 循环来遍历这个 list 或 tuple 

def iterator():
    for ch in 'this is a wonderful world':
        print(ch, end=' ')
    print('\n')

    nums = [1, 2, 3, 4, 5]
    for num in nums:
        print(num, end='')
    print('\n')

    dicts = {'name': 'jim', 'age': 24, 'sex': '男'}
    for key in dicts:
        print(key, end=' ')
    print('\n')

    for value in dicts.values():
        print(value, end='')
    print('\n')

    for (x, y) in [(1, 'a'), (2, 'b'), (3, 'c')]:
        print(x, y)

　　迭代器有两个基本的方法：iter() 和 next(),且字符串，列表或元组对象都可用于创建迭代器，迭代器对象可以使用常规 for 语句进行遍历，也可以使用 next() 函数来遍历。

    nums = [1, 2, 3, 4, 5]
    iterNums = iter(nums)
    while True:
        try:
            print(next(iterNums), end=' ')
        except StopIteration:
            break

实现可迭代对象和迭代器对象

　　需求：从网络抓取各个城市气温信息，并依次显示：

                        北京：15～20

                        天津：17～22

                        长春：12～18

      解决方案：

　　　　Step1：实现一个迭代器对象WeatherIterator，用__next__(方法每次返回一个城市气温

　　　　Step2：实现一个可迭代对象WeatherIterable，用__iter__()方法返回一个迭代器对象

from collections.abc import Iterable, Iterator
import requests


class WeatherIterator(Iterator):

    def __init__(self, cities):
        self.cities = cities
        self.index = 0

    def getWeather(self, city):
        result = requests.get(u'http://wthrcdn.etouch.cn/weather_mini?city=' + city)
        data = result.json()['data']['forecast'][0]
        return '%s:%s,%s' % (city, data['low'], data['high'])

    def __next__(self):
        if self.index == len(self.cities):
            raise StopIteration
        city = self.cities[self.index]
        self.index += 1
        return self.getWeather(city)


class WeatherIterable(Iterable):

    def __init__(self, cities):
        self.cities = cities

    def __iter__(self):
        return WeatherIterator(self.cities)


if __name__ == '__main__':
    for x in WeatherIterable([u'北京', u'上海', u'广州', u'郑州']):
        print(x)

 生成器迭代对象

class PrimeNumber:

    def __init__(self, start, end):
        self.start = start
        self.end = end

    def isPrimeNumber(self, number):
        if number < 2:
            return False
        for x in range(2, number):
            if number % x == 0:
                return False
        return True

    def __iter__(self):
        for x in range(self.start, self.end):
            if self.isPrimeNumber(x):
                yield x


if __name__ == '__main__':
    for x in PrimeNumber(1, 100):
        print(x)

一个班级语文数据英语的总成绩

def total_grade():
    chinese = [randint(60, 100) for _ in range(40)]
    math = [randint(60, 100) for _ in range(40)]
    english = [randint(60, 100) for _ in range(40)]

    total = []
    for (ch, m, eng) in zip(chinese, math, english):
        total.append(ch + m + eng)
    print(total)

三个班大于90分的成绩

def total_grade():
    class1 = [randint(60, 100) for _ in range(40)]
    class2 = [randint(60, 100) for _ in range(40)]
    class3 = [randint(60, 100) for _ in range(40)]

    for x in chain(class1, class2, class3):
        if x > 90:
            print(x)