title: ValueError: unknown url type in urllib2, though the url is fine if opened in a browser
body: <p>Basically, I am trying to download a URL using urllib2 in python.</p>
  
  <p>the code is the following:</p>
  
  <pre><code>import urllib2
  req = urllib2.Request('www.tattoo-cover.co.uk')
  req.add_header('User-agent','Mozilla/5.0')
  result = urllib2.urlopen(req)
  </code></pre>
  
  <p>it outputs ValueError and the program crushes for the URL in the example.
  When I access the url in a browser, it works fine.</p>
  
  <p>Any ideas how to handle the problem?</p>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>thanks for Ben James and sth the problem is detected => add 'http://'</p>
  
  <p>Now the question is refined:
  Is it possible to handle such cases automatically with some builtin function or I have to do error handling with subsequent string concatenation?</p>