Python-сообщество

        self.executor = ThreadPoolExecutor(max_workers=self.threads)
        self.pending = set()
        
        for proxy in proxies:            
            future = self.executor.submit(self.worker, proxy)
            future.add_done_callback(self.process_result)
            self.log('проверяем ' + proxy)
            self.pending.add(future)
            self.app.processEvents()

    def process_result(self, future):
        
        self.pending.discard(future)
    
        if self.stopCheck:
            future.cancel() # или просто делал здесь ретурн
            
        if future.cancelled():
            return

        res, proxy = future.result()                
        
        self.emit(QtCore.SIGNAL("threadDone"), [res, proxy])   # и в threadDone пробовал тоже ставить ретурн

    def worker(self, proxy):
        ''' thread body '''
            
        self.emit(QtCore.SIGNAL("threadStarted"))
        
        if self.stopCheck:       # тоже бестолку
            return [5, proxy]            

        if ':' not in proxy:            
            return [3, proxy]
        
        try:                
            hnd = http.client.HTTPConnection(proxy, timeout=1)
            hnd.request('GET', self.checkUrl, '', {'Content-Type': 'application/x-www-form-urlencoded'})
            body = hnd.getresponse().read().decode(self.charsetToCheck)

            return [1, proxy] if self.checkText in body else [0, proxy]
        except:
            return [4, proxy]

    def stop(self):
        self.stopCheck = True
        self.log('останавливаем проверку')

    def process_result(self, future):
        
        self.pending.discard(future)
    
        if self.stopCheck:
            future.cancel() # или просто делал здесь ретурн
            
        if future.cancelled():
            return

  File "main.py", line 208, in worker
    for f in self.pending:
RuntimeError: Set changed size during iteration