Python urllib.urlretrieve下载图片数据丢失

           今天用Python抓取网页上的图片，发现抓取下来的图片全打不开。代码如下

#!/usr/bin/env python

from pyquery import PyQuery as pq
import urllib
import os
from os.path import split, splitext 
from sys import argv

def get_images(url):
    images = []
    d = pq(url=url)
    p = d('img')
    for  img in p:
        images.append(dict(img.items()))
    return images

class WebImage(object):
    def __init__(self, url=None):
        self.url = url
    def rseturl(self, url):
        self.url = url
    def retrieve(self, dir=None, name=None):
        if self.url is None:
            return
        if dir is None:
            dir = os.getcwd()
        if name is None:
            name = split(self.url)[1]
        else:
            name = name + splitext(self.url)[1]
        self.file = os.path.join(dir, name)
        print 'download', self.url, 'to ', self.file
        urllib.urlretrieve(self.url, self.file)
    def filename(self):
        return self.file
    
def main():
    if len(argv) > 1:
        url = argv[1]
    else:
        try:
            url = raw_input('Enter URL:')
        except (KeyboardInterrupt, EOFError):
            url = ''
    if not url:
        return
    images = get_images(url)
    i = WebImage()
    for img in images:
        i.rseturl(img['src'])
        i.retrieve()

if __name__ == '__main__':
    main()

请问是什么问题？