演示从指定url下载一个mp3文件，并在下载过程中显示出下载进度百分比
#encoding=utf-8
import urllib
import sys
def cbk(a,b,c):
per = 100.0*a*b/c
if per >100:
per=100
def cls(str):
return ‘\r’*len(str)
out=’%.2f%%’%per
sys.stdout.write(u’下载进度：’)
sys.stdout.write(out)
sys.stdout.write(cls(out))
url=””
urllib.urlretrieve(url,’download_123.mp3′,cbk)