Why is this recursion stopping
<p>Im new to python and in my code below: I have a crawler that recurses on new discovered links. After recursing on the root link, it seems like the program is stop after printing a couple of links, this should go on for a while, but its not. I am catching and printing exceptions but the program terminates successful, so im not really sure why its stopping.</p>

<pre><code>from urllib import urlopen
from bs4 import BeautifulSoup

def crawl(url, seen):
    try:
    if any(url in s for s in seen):
       return 0
    html = urlopen(url).read()

    soup = BeautifulSoup(html)
    for tag in soup.findAll('a', href=True):
        str = tag['href']
        if 'http' in str:
        print tag['href']
        seen.append(str)
        print "--------------"
        crawl(str, seen)
    except Exception, e:
      print e
      return 0

def main ():
    print "$ = " , crawl("http://news.google.ca", [])


if __name__ == "__main__":
    main()
</code></pre>
