title: <type 'exceptions.IOError'>: [Errno 13] Permission denied using cElementTree on appengine
body: <p>Trying to grab an xml file from an internet source and parse it for some values.
  My code:</p>
  
  <pre><code>def get_xml(self):
  
      #xml_url =   "http://www.shoppingcar.it/feed/export_vel.asp?parametro=1"
      xml_url =   "http://dl.dropbox.com/u/102727/AutoVeloce%20XML%20Splitter/shoppingcar.xml"
  
      MAX_RETRY = 3
      retry_left = MAX_RETRY
  
      while retry_left:
          try:
              req =   urlfetch.fetch(xml_url, deadline=10)
              XML =   req.content.decode('windows-1252')
              break   # &lt;- done! got file.
  
          except (urllib2.HTTPError, DownloadError):
              retry_left -= 1
              logging.error("Error while downloading ShoppingCar.xml, retrying.")
          except DeadlineExceededError:
              retry_left -= 1
              logging.warning("DeadlineExceededError while downloading ShoppingCar.xml, retrying.")
          except Timeout:
              retry_left -= 1
              logging.warning("Timeout while downloading ShoppingCar.xml, retrying.")
  
      if retry_left and retry_left &lt; MAX_RETRY:
          logging.info("Downloading ShoppingCar.xml succeeded after %s retries.", MAX_RETRY - retry_left)
      if not retry_left:
          logging.error("Downloading ShoppingCar.xml failed after %s retries.", MAX_RETRY)
  
      return ET.parse(XML)
  
  def _iter_carDicts_in_xml(self, newOnly=True):
  
      #fails here &gt;
      tree = self.get_xml()
  
      for veicolo in tree.getiterator('veicolo'):
          # do stuff
  </code></pre>
  
  <p>Error message I get:</p>
  
  <pre><code>&lt;type 'exceptions.IOError'&gt;: [Errno 13] Permission denied: u'&lt;?xml version="1.0" encoding="windows-1252"?&gt;&lt;veicoli&gt;\r\n    &lt;veicolo&gt;\r\n\t\t&lt;id&gt;&lt;![CDATA[26806]]&gt;&lt;/id&gt;
  </code></pre>
  
  <p>This error continues spitting out the xml file so i won't paste it all</p>
  
  <p>Really not sure where to go on this one, I've used similar code to extract from xml files and never had this kind of problem. Any ideas?</p>