来源：Udacity《编程基础：Python》课程2
功能：每隔30分钟，打开特定网页来提醒休息
# coding:utf-8
import webbrowser
import time
total_breaks = 3
break_count = 0
print "\nThis program started on: " + time.ctime() # time.ctime():current time(sec)
while break_count <= total_breaks:
time.sleep(30 * 60） # time.sleep():sleep time(sec) ,30 min
print "\nBreak Time!\t" + time.ctime()
webbrowser.open("https://cn.udacity.com/course/programming-foundations-with-python--ud036") # 开网页
break_count = break_count + 1