How to create a function that counts total string objects in my ArrayField column for my model?

Trying to create a column in my model called, stock_count, that finds the sum of the total string objects in my ArrayField(), aka stock_list. Here is my function.

    def total_stocks_calc(self):
        self.stock_count = Bucket.objects.aggregate(Sum('stock_list', distinct=True))
        self.save()

However it doesn't seem to be doing anything, no calculating, leaving the field blank in my model, admin page, and DRF interface...

EDIT: updated post with new implementation.

Here is my model.

class Bucket(models.Model):


    owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name='buckets')
    users = models.ManyToManyField(settings.AUTH_USER_MODEL)
    category = models.CharField(max_length=30, choices=category_options)
    name = models.CharField(max_length=35)
    created = models.DateTimeField(default=timezone.now)
    slug = models.SlugField(unique=True, blank=True) 
    stock_count = models.IntegerField(blank=True, null=True)
    stock_list = ArrayField(models.CharField(max_length=6,null=True),size=30,null=True)
    about = models.CharField(max_length=75)

    objects = models.Manager()
    bucketobjects = BucketObjects()

    class Meta:
        ordering = ('-created',)

    def total_stocks_calc(self):
        self.stock_count = Bucket.objects.annotate(stock_count=F('stock_list__len'))
        self.save()


    def __unicode__(self):
        return self.stock_list

Would like to know the proper way to count total items in ArrayField(), thank you in advance.