Attribute error when using Python multithreading

Question

I get an error:

AttributeError: 'Park_Stat_Thread' object has no attribute 'park_stat

when I run the script below. Any idea how to pass back the park_stat variable?

As you can see I use multi-threading to crawl a list of URLs from the web:

class Park_Stat_Thread(Thread):

    def __init__(self, thread_num):
        super().__init__()
        self.thread_num = thread_num

    def run(self):
        print('starting thread %s.' % self.thread_num)
        process_queue(self)
        print('exiting thread %s.' % self.thread_num)

    def process_queue(self):
        while True:
            try:
                x = my_queue.get(block=False)

            except queue.Empty:
                return

            else:
                parking_stat_getter(self,x)

            time.sleep(1)

    def parking_stat_getter(self,x):
        base = 'http://www.ahuzot.co.il/Parking/ParkingDetails/?ID={}'
        response = requests.get(base.format(self.thread_num))
        soup = BeautifulSoup(response.text, "lxml")

        try:

            self.park_stat = 0
            for img in soup.find_all('img' , attrs={'src': re.compile("ParkingIcons")}):
                soup_img = str(img)

                if 'male' in soup_img:
                    self.park_stat=1
                elif 'meat' in soup_img:
                    self.park_stat=2
                elif 'panui' in soup_img:
                    self.park_stat=3  

        except AttributeError:
          self.park_stat = np.nan

        return self.park_stat

def get_parkings_Stat(parking_id_lists):
    threads = [Park_Stat_Thread(t) for t in range(1, 8)]  

    for thread in threads:        
        thread.start()
    for thread in threads:
        thread.join()

    park_details = dict(zip(parking_id_lists, [thread.park_stat for thread in threads]))

    return park_details

I think the problem is that you need to include the park_stat property in the class initialisation too. I think it's not possible to create class properties on the go, but you can modify them on the go. — boomkin
– boomkin, Commented Mar 14, 2020 at 21:51
if I add it, then it will be asked as input when I call the thread Park_Stat_Thread(t), but its not an input rather the output. — Amir Kachln
– Amir Kachln, Commented Mar 15, 2020 at 12:47
Don't look at it as input-output, but rather like Age for a typical example of class People(). Every new born is initialised as person.Age=0 , but modified every year. Here, I think you could do the same, but you have to make sure that the "modification" is done already, before calling the getter for that property. — boomkin
– boomkin, Commented Mar 15, 2020 at 12:51

boomkin · Accepted Answer · 2020-03-15 16:13:23Z

You are missing a class attribute from the class constructor. You cannot declare a class attribute later, but you can set it to some dummy value.

class Park_Stat_Thread(Thread):

    def __init__(self, thread_num):
        super().__init__()
        self.thread_num = thread_num
        self.park_stat = 0


    def run(self):
        print('starting thread %s.' % self.thread_num)
        process_queue(self)
        print('exiting thread %s.' % self.thread_num)

    def process_queue(self):
        while True:
            try:
                x = my_queue.get(block=False)

            except queue.Empty:
                return

            else:
                parking_stat_getter(self,x)

            time.sleep(1)

    def parking_stat_getter(self,x):
        base = 'http://www.ahuzot.co.il/Parking/ParkingDetails/?ID={}'
        response = requests.get(base.format(self.thread_num))
        soup = BeautifulSoup(response.text, "lxml")

        try:

            self.park_stat = 0
            for img in soup.find_all('img' , attrs={'src': re.compile("ParkingIcons")}):
                soup_img = str(img)

                if 'male' in soup_img:
                    self.park_stat=1
                elif 'meat' in soup_img:
                    self.park_stat=2
                elif 'panui' in soup_img:
                    self.park_stat=3  

        except AttributeError:
          self.park_stat = np.nan

        return self.park_stat

def get_parkings_Stat(parking_id_lists):
    threads = [Park_Stat_Thread(t) for t in range(1, 8)]  

    for thread in threads:        
        thread.start()
    for thread in threads:
        thread.join()

    park_details = dict(zip(parking_id_lists, [thread.park_stat for thread in threads]))

    return park_details

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