python - Object of type NoneType using threads -

i have following class

queue = queue.queue() class spectraprocessing(threading.thread):     def __init__(self, queue, pbar = none, image_infos = []):         threading.thread.__init__(self)         self.queue = queue         self.pbar = pbar         self.image_infos = image_infos      def run(self):         while true:         spectrum = self.queue.get()         self.image_infos.append(get_spectruminfos(spectrum))          #signal queue job has been done         if self.pbar:             self.pbar.update(self.pbar.currval + 1)         self.queue.task_done() 

msrun iterator on spectrum objects created class reader:

msrun = pimzml.run.reader(file_imzml, file_ibd, msn_precision = 250e-6) 

each spectrum object has attribute list will(initially []) contains intensities (float values). main function contain this:

number_spectra = len(msrun)    print "start creating image spectra..." pbar = progressbar( maxval = number_spectra ).start()  #spawn pool of threads, , pass them queue instance image_infos = [] in range(number_spectra):     t = spectraprocessing(queue, pbar, image_infos)     t.setdaemon(true)     t.start() #populate queue data spectrum in msrun:     queue.put(spectrum)  #wait on queue until has been processed queue.join() 

get_spectruminfos(spectrum) function called run method, handles (fill list intensities, ...) list of intensities of each spectrum. when execute error list of intensities nonetype (i.e.; empty), times execution doing without error. without using threads there no error.

thank lot.