# -*- utf-8 -*-
"""
实际用例:
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
.....
如果依次抓取所有城市天气再显示,显示第一个城市气温时,有很高的延时,
并且浪费存储空间.我们期望以"用时访问"的策略,并且能把所有城市气温封装到一个对象里,
可用for语句进行迭代.
解决方案:
step1:实现一个迭代器对象WeatherIterator,next方法每次返回一个城市气温
step2:实现一个可迭代对象WeatherIterator,__iter__方法返回一个迭代器对象.
"""
l = [1, 2, 3, 4]
s = 'abcde'
for x in l:print(x)
for x in s:print(x)
# l, s(可迭代对象) ---iter()-->迭代器对象
# iter(l)实际调用的是l.__iter__()
# iter(s)实际调用的是s.__getitem__()
from collections import Iterable, Iterator
print(Iterator.__abstractmethods__) # 查看迭代器的抽象接口
# frozenset({'__next__'})
print(Iterable.__abstractmethods__) # 查看可迭代对象的抽象接口
# frozenset({'__iter__'})
import requests
class WeatherIterator(Iterator):
def __init__(self, cities):
self.cities = cities
self.index = 0
def getWeather(self, city):
r = requests.get(u'http://wthrcdn.etouch.cn/weather_mini?city=' + city)
data = r.json()['data']['forecast'][0]
return '%s: %s , %s ' % (city, data['low'], data['high'])
def __next__(self): # 重写了父类中的__next__()方法
if self.index == len(self.cities):
raise StopIteration # 迭代到最后一个对象后抛出的异常,用于停止迭代
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): # 重写了父类中的__iter__()方法
return WeatherIterator(self.cities)
for x in WeatherIterable([u'北京', u'上海', u'广州', u'邢台', u'长春']):
print(x)
3-1 实现可迭代对象和迭代器对象
最新推荐文章于 2022-11-02 16:22:07 发布
