python提取网页源代码的图像链接网址为什么失败？

代码如下，请高手指教
def getHTMLlines(htmlpath):
    f=open(htmlpath,'r',encoding='utf-8')
    ls=f.readlines()
    f.close()
    return ls

def extractImageUrls(htmllist):
    urls=[]
    for line in htmllist:
        if 'a' in line:
            url=line.split('href=')[-1].split('"')[0]

            if 'http' in url:
                urls.append(url)
    return urls

def showResults(urls):
    count=0
    for url in urls:
        print('第{:2}个URL:{}'.format(count,url))
        count+=1

def saveResults(filepath,urls):
    f=open(filepath,'w')
    for url in urls:
        f.write(url+'\n')
    f.close()

def main():
    intputfile='baidu3.html'
    outputfile='baidu3-urls.txt'
    htmlLines=getHTMLlines(intputfile)
    imageUrls=extractImageUrls(htmlLines)
    showResults(imageUrls)
    saveResults(outputfile,imageUrls)

main()