title: python Gtk.PrintOperation print a pdf
body: <p>Until now i was using a variant of this code to print a pdf that i create with pisa.</p>
  
  <p>That is taken from pygtk faq:</p>
  
  <pre><code>import gtk
  import gtkunixprint
  
  def print_cb(printjob, data, errormsg):
      if errormsg:
          print('Error occurred while printing:\n%s' % errormsg)
  
  filename = 'the_pdf_file_to_be_printed.pdf'
  pud = gtkunixprint.PrintUnixDialog()
  response = pud.run()
  if response == gtk.RESPONSE_OK:
      printer = pud.get_selected_printer()
      settings = pud.get_settings()
      setup = pud.get_page_setup()
      printjob = gtkunixprint.PrintJob('Printing %s' % filename, printer, settings, setup)
      printjob.set_source_file(filename)
      printjob.send(print_cb)
  pud.destroy()
  </code></pre>
  
  <p>Now i am porting to Gtk3 PyObject and i can't solve the problem. 
  I found that Gtk.PrintOperation is the way but i can't relate print Operation whith a printJob or how  to pass the file to print.<br>
  thanks </p>