使用python beautifulsoup提取图像

Question

我使用以下方法从Amazon列表中提取所需的HTML：

import requests
from bs4 import BeautifulSoup

r=requests.get("http://www.amazon.com/dp/B0007RXSB4")
r.content

soup=BeautifulSoup(r.content)

soup.find_all("div", {"id":"imgTagWrapperId"})

给了我这个：

[<div class="imgTagWrapper" id="imgTagWrapperId">\n<img alt="Johnston         
&amp; Murphy Men's Greenwich Oxford,Black,6 D" class="a-dynamic-image 
a-stretch-vertical" data-a-dynamic-image='{"http://ecx.images-
amazon.com/images/I/81zwayZox-S._UY695_.jpg":
[695,695],"http://ecx.images-amazon.com/images/I/81zwayZox-
S._UY535_.jpg":[535,535],"http://ecx.images-
amazon.com/images/I/81zwayZox-S._UY500_.jpg":
[500,500],"http://ecx.images-amazon.com/images/I/81zwayZox-
S._UY575_.jpg":[575,575],"http://ecx.images-
amazon.com/images/I/81zwayZox-S._UY395_.jpg":
[395,395],"http://ecx.images-amazon.com/images/I/81zwayZox-
S._UY585_.jpg":[585,585]}' data-old-hires="http://ecx.images-
amazon.com/images/I/81zwayZox-S._UL1500_.jpg" id="landingImage" 
onload="this.onload='';setCSMReq('af');if(typeof addlongPoleTag === 
'function'){ addlongPoleTag('af','desktop-image-atf-
marker');};setCSMReq('cf')" src="http://ecx.images-
amazon.com/images/I/41KixMIlPNL._SY395_QL70_.jpg" style="max-
width:695px;max-height:695px;">\n</img></div>]

我只需要知道如何从上面的代码中提取http://ecx.images-amazon.com/images/I/81zwayZox-S._UY695_.jpg。