====== Python Regular Expressions ======

<code>
>>> urls = r'/node/(\d)'
>>> regex = re.compile(urls)
>>> regex.search('/node/122').group()
'/node/1'
>>> regex.search('/node/122').group(1)
'1'
</code>

  * define the pattern.
  * compile, python will return regex object
  * use the search method, pass the string we wanna search for.
  * match object will be return if the pattern found.
  * use .group() method of match object to pull out matching group.