Python 迭代器与生成器实例详解迭代器与生成器实例详解
Python 迭代器与生成器实例详解迭代器与生成器实例详解
一、如何实现可迭代对象和迭代器对象
1.由可迭代对象得到迭代器对象
例如l就是可迭代对象，iter(l)是迭代器对象
In [1]: l = [1,2,3,4]
In [2]: l.__iter__
Out[2]: <method-wrapper '__iter__' of list object at 0x000000000426C7C8>
In [3]: t = iter(l)
In [4]: t.next()
Out[4]: 1
In [5]: t.next()
Out[5]: 2
In [6]: t.next()
Out[6]: 3
In [7]: t.next()
Out[7]: 4
In [8]: t.next()
---------------------------------------------------------------------------
StopIteration Traceback (most recent call last)
<ipython-input-8-3660e2a3d509> in <module>()
----> 1 t.next()
StopIteration:
for x in l：
print x
for 循环的工作流程，就是先有iter(l)得到一个t，然后不停的调用t.nex(),到最后捕获到StopIteration，就结束迭代
# 下面这种直接调用函数的方法如果数据量大的时候会对网络IO要求比较高，可以采用迭代器的方法
def getWeather(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'])
print getWeather(u'北京')
返回值：
北京:低温 13℃,高温 28℃
实现一个迭代器对象WeatherIterator,next 方法每次返回一个城市气温
实现一个可迭代对象WeatherIterable,iter方法返回一个迭代器对象
# -*- coding:utf-8 -*-
import requests
from collections import Iterable, Iterator
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):
if self.index == len(self.cities):
raise StopIteration
city = self.cities[self.index] self.index += 1
return self.getWeather(city)
class WeatherIterable(Iterable):
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