title: python: find html tags and replace their attributes
body: <p>I need to do the following:</p>
  
  <ol>
  <li>take html document</li>
  <li>find every occurrence of 'img' tag</li>
  <li>take their 'src' attribute</li>
  <li>pass founded url to processing</li>
  <li>change the 'src' attribute to the new one</li>
  <li>do all this stuff with Python 2.7</li>
  </ol>
  
  <p>P.S. I,ve heard about lmxl and BeautifulSoup. How do you recommend to solve this problem with? Maybe it would be better to use regexes then? or another something else? </p>