title: How can I resolve a "[Errno 13] file not accessible" error?
body: <p>My web application uses Django (django-nonrel) on Google App Engine. I am trying to open a Blobstore file. </p>
  
  <p>My code successfully creates the Blobstore file and a Photo object to refer to the Blobstore's file name (along with some other metadata).</p>
  
  <pre><code>from __future__ import with_statement
  from google.appengine.api import files
  import mimetypes
  
  ...
  
    file_name = files.blobstore.create(mime_type=mimetypes.guess_type(request.FILES['photo'].name)[0])
  
    with files.open(file_name, 'a') as f:
      f.write(photo_data)
  
    files.finalize(file_name)
  
    photo = Photo()
    photo.file_name = file_name
    ...
    photo.save()
  </code></pre>
  
  <p>However, trying to open the file produces the following error:</p>
  
  <pre><code>opened_file = open(photo.file_name)
  </code></pre>
  
  <blockquote>
    <p>IOError at /post_photo_to_facebook/</p>
    
    <p>[Errno 13] file not accessible: '/blobstore/writable:NDNFUjNIVDdVQTM4Rk9aSE1aQkJMUzJUMzVDRVNRVEhJSjU3RUhWOE9ZMkk3QlNWR0FDR0JDOFUxSlA0Wlk3MA=='</p>
  </blockquote>
  
  <p>Any help is appreciated - thanks for reading!</p>