8、如何实现可迭代对象和迭代器对象
PS：注意重载Iterator方法的时候，需要和原来的方法名一样，否则创建实例时会报错
from collections import Iterator,Iterable
import requests,json class WeatherItertor(Iterator):
def __init__(self,city_list):
self.CityList = city_list
self.indexA = 0 def getWeather(self,city):
r = requests.get('http://www.weather.com.cn/data/sk/{code}.html'.format(code=city))
ret = json.loads(r.content.decode("utf-8"))
#风向
WD = ret["weatherinfo"]["WD"]
#城市
city_data = ret["weatherinfo"]["city"]
return "城市：{city},风向：{WD}".format(city=city_data,WD=WD) def __next__(self):
if self.indexA == len(self.CityList):
raise StopIteration
city = self.CityList[self.indexA]
self.indexA += 1
return self.getWeather(city) class WeatherIterable(Iterable):
def __init__(self,city_list):
self.CityList =city_list def __iter__(self):
return WeatherItertor(self.CityList) # citys = {'北京':101010100,'朝阳':101010300,'顺义':101010400,'怀柔':101010500}
citys_list = [101010100,101010300,101010400,101010500]
ret = WeatherIterable(citys_list) for x in ret:
print(x) result:
C:\Python35-32\python.exe C:/laoni/PycharmProjects/TEXT/aa.py
城市：北京,风向：东南风
城市：朝阳,风向：南风
城市：顺义,风向：南风
城市：怀柔,风向：西南风
9、如何使用生成器函数实现可迭代对象
函数里有yield关键是，则是生成器，生成器内置有__iter__方法，只不过调用__iter__返回的是生成器本身，利用这一特性，可以创建一个可迭代对象的类。
class PrimeNum():
def __init__(self,start,end):
self.start = start
self.end = end def aa_bb(self,x):
if x % 2 ==0:
ret = "这是一个偶数：{info}".format(info=x)
elif x % 2 !=0:
ret = "这是一个奇数：{info}".format(info=x)
else:
pass
return ret def __iter__(self):
for x in range(self.start,self.end):
p = self.aa_bb(x)
yield p for x in PrimeNum(1,8):
print(x) result：
这是一个奇数：1
这是一个偶数：2
这是一个奇数：3
这是一个偶数：4
这是一个奇数：5
这是一个偶数：6
这是一个奇数：7
10、如何进行反向迭代以及如何实现反向迭代
正向的可以使用iter函数获取正向的迭代器，reversed函数可以获取反向的迭代器，使用reversed的前提是对象本身具有__reversed__方法
class FloatRange():
def __init__(self,start,end,step=0.2):
self.start =start
self.end = end
self.step = step def __iter__(self):
t = self.start
while t <= self.end:
yield t
t += self.step def __reversed__(self):
t = self.end
while t >= self.start:
yield t
t -= self.step for x in reversed(FloatRange(1,4)):
print(x) 结果：
4
3.8
3.5999999999999996
3.3999999999999995
3.1999999999999993
2.999999999999999
2.799999999999999
2.5999999999999988
2.3999999999999986
2.1999999999999984
1.9999999999999984
1.7999999999999985
1.5999999999999985
1.3999999999999986
1.1999999999999986
11、如何对迭代器做切片操作
通过readlines方法可以获取到，
f = open('H2','r')
print(f)
ret = f.readlines()
print(ret[1:3])
result：
<_io.TextIOWrapper name='H2' mode='r' encoding='cp936'>
[' log 127.0.0.1 local2\n', ' daemon\n']
使用itertools.islice
from itertools import islice
f = open('H2','r')
#获取第10到第20行
info = islice(f,10,20)
print(info)
for x in info:
print(x)
#获取开始到第二十行
info2 = islice(f,30)
#获取第四十行到结尾
info3 = islice(f,40,None)
retsult：
<itertools.islice object at 0x01803F00>
timeout server 50000ms
option dontlognull
listen scats :8888
stats enable
stats uri /admin
stats auth admin:1234
frontend oldboy.org
bind 0.0.0.0:80
option httplog
12、如何在一个for语句中迭代多个可迭代对象
from random import randint
from itertools import chain #并行
Chinese = [randint(40,100) for x in range(10)]
Math = [randint(50,100) for x in range(10)]
English = [randint(60,100) for x in range(10)]
print(Chinese,Math,English)
result = []
for C,M,E in zip(Chinese,Math,English):
ret = C + M + E
result.append(ret) print(result) #串行
class_one = [randint(40,100) for x in range(6)]
class_two = [randint(50,100) for x in range(8)]
class_three = [randint(60,100) for x in range(9)]
chin = 0
for x in chain(class_one,class_two,class_three):
if x >= 90:
chin += 1 print(chin)