今天學習了使用python編寫爬蟲程式，從中國天氣網爬取杭州的天氣。使用到了urllib庫和bs4。bs4提供了專門針對html的解析功能，比用RE方便許多。

# coding : UTF-8
import sys
reload(sys)
sys.setdefaultencoding( "utf-8" )
from bs4 import BeautifulSoup
import csv
import urllib


def get_html(url):
    html = urllib.urlopen(url)
    return html.read()

def get_data(html_text)
 
:
    final = []
    bs = BeautifulSoup(html_text, "html.parser")
    body = bs.body
    data = body.find('div', {'id': '7d'})
    ul = data.find('ul')
    li = ul.find_all('li')

    for day in li:
        temp = []
        date = day.find('h1').string
        temp.append(date)
        inf = day.find_all('p'
 
)
        temp.append(inf[0].string,)
        if inf[1].find('span') is None:
            temperature_highest = None
        else:
            temperature_highest = inf[1].find('span').string
            temperature_highest = temperature_highest.replace('C', '')
        temperature_lowest = inf[1].find('i'
 
).string
        temperature_lowest = temperature_lowest.replace('C', '')
        temp.append(temperature_highest)
        temp.append(temperature_lowest)
        final.append(temp)

    return final


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

if __name__ == '__main__':
    html_doc = get_html('http://www.weather.com.cn/weather/101190401.shtml')
    result = get_data(html_doc)
    write_data(result, 'weather.csv')
    print result

執行結果儲存在csv檔案中，如下：

28日（今天）,小雨,,13℃
29日（明天）,小雨轉陰,15℃,12℃
30日（後天）,多雲,19℃,14℃
31日（週一）,小雨,16℃,14℃
1日（週二）,陰轉多雲,16℃,10℃
2日（週三）,多雲轉晴,17℃,10℃
3日（週四）,多雲轉晴,18℃,11℃