1. 每分钟抓取一次课程页面学习人数.
2. 和前次进行对比, 数量增加意味课程卖出, 播放本地音乐.
3. 同时监听多们课程.

from threading import Timer
from scrapy.selector import Selector
from subprocess import getoutput
import requests

COURSES = {
        # Python高级编程技巧实战
        62: {
            'url': 'http://coding.imooc.com/class/62.html',
            'mp3': 'happy.mp3',
        },

        75: {
            'url': 'http://coding.imooc.com/class/75.html',
            'mp3': 'happy2.mp3',
        },

        74: {
            'url': 'http://coding.imooc.com/class/74.html',
            'mp3': 'happy3.mp3',
        },
}

def getSalesVolume(courses):
    res = {}
    for course in courses:
        url = COURSES[course]['url']
        response = requests.get(url)
        sel = Selector(text=response.text)

        sv = sel.css('div.static-item:nth-child(3) > \
                span.meta-value > strong::text').extract_first()
        res[course] = int(sv)
    return res

def loop(courses, svOld):
    try:
        sv = getSalesVolume(courses)
        for course in courses:
            print(course, svOld[course], sv[course])
            cmd = 'play %s' % COURSES[course]['mp3']
            for _ in range(sv[course] - svOld[course]):
                getoutput(cmd)
        svOld = sv
    except IOError as e:
        print(e)

    Timer(60, loop, args=(courses, svOld)).start()

courses = [62, 75, 74]
loop(courses, getSalesVolume(courses))