title: Python's `urllib2`: Why do I get error 403 when I `urlopen` a Wikipedia page?
body: <p>I have a strange bug when trying to <code>urlopen</code> a certain page from Wikipedia. This is the page:</p>
  
  <p><a href="http://en.wikipedia.org/wiki/OpenCola_(drink)" rel="noreferrer">http://en.wikipedia.org/wiki/OpenCola_(drink)</a></p>
  
  <p>This is the shell session:</p>
  
  <pre><code>&gt;&gt;&gt; f = urllib2.urlopen('http://en.wikipedia.org/wiki/OpenCola_(drink)')
  Traceback (most recent call last):
    File "C:\Program Files\Wing IDE 4.0\src\debug\tserver\_sandbox.py", line 1, in &lt;module&gt;
      # Used internally for debug sandbox under external interpreter
    File "c:\Python26\Lib\urllib2.py", line 126, in urlopen
      return _opener.open(url, data, timeout)
    File "c:\Python26\Lib\urllib2.py", line 397, in open
      response = meth(req, response)
    File "c:\Python26\Lib\urllib2.py", line 510, in http_response
      'http', request, response, code, msg, hdrs)
    File "c:\Python26\Lib\urllib2.py", line 435, in error
      return self._call_chain(*args)
    File "c:\Python26\Lib\urllib2.py", line 369, in _call_chain
      result = func(*args)
    File "c:\Python26\Lib\urllib2.py", line 518, in http_error_default
      raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)
  urllib2.HTTPError: HTTP Error 403: Forbidden
  </code></pre>
  
  <p>This happened to me on two different systems in different continents. Does anyone have an idea why this happens?</p>