print("Hello World!") import re # relative to absolute strs = '<img id="img_zhaoliying" src="img/zhangliying.png" title="赵丽颖"/>'; ret = re.sub(r'(?P<img><img[^>]+?src=")',"\g<img>http://www.baidu.com/",strs); #count,flags print(ret) # add preffix ret = re.sub(r'(?P<img><img[^>]+?)src',"\g<img>data-src",strs); #count,flags print(ret)