title: Problems generating pdf from HTML with Pisa (Python)
body: <p>In my web app, writen in django, I met the need to convert an html
  template in a pdf document. 
  I decided to use Pisa and this is the incriminated code:</p>
  
  <p>myview.py:</p>
  
  <pre><code>#view.py
  ...
  import ho.pisa as pisa
  import cStringIO as StringIO #pdf
  ...
  @login_required 
  def dettaglio_bolla(request, id=None, tipo=None):
          bolla = Bolla.objects.get(id = id)
      cliente = Cliente.objects.get(id = bolla.destinatario.id)
      allegati = Allegato.objects.filter(bolla = bolla)
      paginator = Paginator(allegati, 2)
      try:
          pagina = int(request.GET.get('pagina','1'))
      except ValueError:
          pagina = 1
      try:
          pagina_allegati = paginator.page(pagina)
      except (EmptyPage, InvalidPage):
          pagina_allegati = paginator.page(paginator.num_pages)
      response =  render_to_response("dettaglio_bolla.html",{'bolla':bolla,'cliente':cliente,'allegati': pagina_allegati})
      if tipo == ".pdf":
          result = StringIO.StringIO()
          pisa.CreatePDF(unicode(response.content,encoding="utf-8"), result)
          return HttpResponse(result.getvalue(), mimetype='application/pdf')
      return response
  </code></pre>
  
  <p>The PDF is generated but all I get is a blank page. Did I miss something?
  I checked the official tutorials but I can't figure it out.</p>