python3.5爬虫实例：根据城市名称来获取该城市最近七天的天气预报

#抓取天气网站最近7天的天气情况，写入文件并在控制台显示
from bs4 import BeautifulSoup   #用来代替正则表达式取源码中相应标签的内容
import random
import requests #用来抓取网页的html源代码
import socket #用做异常处理
import time
import http.client #用做异常处理
import csv

def get_html(url,data=None):
"""
模拟浏览器来获取网页的html代码
"""
header={
'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8',
'Accept-Encoding': 'gzip, deflate, sdch',
'Accept-Language': 'zh-CN,zh;q=0.8',
'Connection': 'keep-alive',
'User-Agent': 'Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/43.0.235'
}
#设定超时时间，取随机数是因为防止被网站认为是爬虫
timeout=random.choice(range(80,180))
while True:
try:
rep=requests.get(url,headers=header,timeout=timeout)
rep.encoding="utf-8"
break
except socket.timeout as e:
print("3:",e)
time.sleep(random.choice(range(8,15)))

except socket.error as e:
print("4:",e)
time.sleep(random.choice(range(20,60)))
except http.client.BadStatusLine as e:
print("5:",e)
time.sleep(random.choice(range(30,80)))

except http.client.IncompleteRead as e:
print("6:",e)
time.sleep(random.choice(range(5,15)))

return rep.text

def get_data(html_txt):
final=[]
bs=BeautifulSoup(html_txt,"html.parser")   #创建BeautifulSoup对象
body=bs.body   #获取body部分
data=body.find("div",{"id":"7d"}) #找到id为7d的div
ul=data.find("ul")  #获取ul部分
li=ul.find_all("li")   #获取所有的li

for day in li:  #对每个标签中的内容进行遍历
temp=[]
date=day.find("h1").string   #获取日期
temp.append(date)   #将日期添加到temp 中
inf=day.find_all("p")   #找到li中的所有p标签
temp.append(inf[0].string)   #将第一个p标签中的内容添加到temp列表中红
if inf[1].find("span") is None:
temperature_high=None   #傍晚没有最高气温
else:
temperature_high=inf[1].find("span").string  #最高气温
temperature_high=temperature_high.replace("℃","")
temperature_lower=inf[1].find("i").string   #找到最低温
temperature_lower=temperature_lower.replace("℃","")
temp.append(temperature_high)
temp.append(temperature_lower)
final.append(temp)   #将temp添加到final中

return final

def write_data(data, name):
file_name = name
with open(file_name, 'a', errors='ignore', newline='') as f:
f_csv = csv.writer(f)
f_csv.writerows(data)

def get_url():
city={
"海口":"101310101",
"三亚":"101310201",
"苏州":"101190401",
"郑州":"101180101"
}
for k in city:
print(k)
city_name=input("请输入你要查询的城市名字：")
city_num=city[city_name]
weather_url="http://www.weather.com.cn/weather/%s.shtml"%city_num
return weather_url

if __name__=="__main__":
# url="http://www.weather.com.cn/weather/101190401.shtml"
url=get_url()
html=get_html(url)
result=get_data(html)
write_data(result,"weather.csv")
for i in result:
print(i)        #打印天气情况