思路：
1.寻找入口
2.寻找数据所在url
3.获取源码，提取数据
4.数据保存输出

1.入口

入口

通过40天预报可以追溯2016年和2017年全年的天气数据。

2.构造url

分析可知40天的天气数据是通过js异步加载，每个月份对应一个url

url

url由年份和月份组成，我们可以根据这个规律构造url，循环抓取数据

month = ['01','02','03','04','05','06','07','08','09','10','11','12']
    for i in month:
        url = 'http://d1.weather.com.cn/calendar_new/'+str(year)+'/101180101_'+str(year)+str(i)+'.html?_=1496558858156'

3.数据提取

请求url获取的数据是json格式，稍加处理转换为列表，方便提取所需数据。

数据

html = requests.get(url,headers=headers).content
    # print html
    datas = json.loads(html[11:])

切片是为了去除var fc40 =
转换之后就可以用python列表的方法提取所需数据

4.数据保存

数据保存采用.csv格式，用的py2.7,存入中文要用codecs做编码处理

完整代码

# -*- coding:utf-8 -*-
import requests
from lxml import etree
import json
import csv
import codecs
import sys
reload(sys)
sys.setdefaultencoding('utf8')

# url = 'http://d1.weather.com.cn/calendar_new/2017/101010100_201705.html?_=1496558858156'
# headers = {
#     'User-Agent':'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.110 Safari/537.36',
#     'Referer':'http://www.weather.com.cn/weather40d/101010100.shtml'
# }
def getHtml(url):
    html = requests.get(url,headers=headers).content
    # print html
    datas = json.loads(html[11:])
    # print datas
    return datas

def getData(url):

    datas = getHtml(url)
    for data in datas:
        date = data['date']
        hgl = data['hgl']
        hmax = data['hmax']
        hmin = data['hmin']
        date2 = data['nlyf'] + data['nl']
        alins = data['alins']
        als = data['als']
        print date,hgl,hmax,hmin,date2,alins,als
        with open('weather_zz.csv','ab') as f:
            writer = csv.writer(f)
            writer.writerow([date,hgl,hmax,hmin,date2,alins,als])


# a = getData(url)

if __name__ == '__main__':
    # url = 'http://d1.weather.com.cn/calendar_new/2017/101010100_201705.html?_=1496558858156'
    headers = {
        'User-Agent':'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.110 Safari/537.36',
        'Referer':'http://www.weather.com.cn/weather40d/101010100.shtml'
    }

    with open('weather_zz.csv', 'wb') as f:
        f.write(codecs.BOM_UTF8)
        writer = csv.writer(f)
        writer.writerow(['日期', '降水概率', '最高温度', '最低温度', '农历日期', '宜', '不宜'])
    year = input('请输入年份:')
    month = ['01','02','03','04','05','06','07','08','09','10','11','12']
    for i in month:
        url = 'http://d1.weather.com.cn/calendar_new/'+str(year)+'/101180101_'+str(year)+str(i)+'.html?_=1496558858156'
        getData(url)

结果

采用csv写入时，容易出现空行，采用binary模式可以避免，比如wb,ab

with open('weather_zz.csv','ab') as f:

结果

可以获取到20180106的数据