django: RecursionError when initialize a object
Question: SO I am trying to build a simple shopping cart feature for my app, that simply
add, remove a piece of equipment, and display a list of current cart. Here are
my codes for this cart: (codes largely adopted from
<https://github.com/bmentges/django-cart>)

cart.py:

    
    
    import datetime
    from .models import Cart, Item, ItemManager
    
    CART_ID = 'CART-ID'
    
    class ItemAlreadyExists(Exception):
        pass
    
    class ItemDoesNotExist(Exception):
        pass
    
    class Cart:
        def __init__(self, request, *args, **kwargs):
            super(Cart, self).__init__()
            cart_id = request.session.get(CART_ID)
            if cart_id:
                try:
                    cart = models.Cart.objects.get(id=cart_id, checked_out=False)
                except models.Cart.DoesNotExist:
                    cart = self.new(request)
            else:
                cart = self.new(request)
            self.cart = cart
    
        def __iter__(self):
            for item in self.cart.item_set.all():
                yield item
    
        def new(self, request):
            cart = Cart(request, creation_date=datetime.datetime.now())
            cart.save()
            request.session[CART_ID] = cart.id
            return cart
    
        def add(self, equipment):
            try:
                item = models.Item.objects.get(
                    cart=self.cart,
                    equipment=equipment,
                )
            except models.Item.DoesNotExist:
                item = models.Item()
                item.cart = self.cart
                item.equipment = equipment
                item.save()
            else: #ItemAlreadyExists
    
                item.save()
    
        def remove(self, equipment):
            try:
                item = models.Item.objects.get(
                    cart=self.cart,
                    equipment=equipment,
                )
            except models.Item.DoesNotExist:
                raise ItemDoesNotExist
            else:
                item.delete()
    
        def count(self):
            result = 0
            for item in self.cart.item_set.all():
                result += 1 * item.quantity
            return result
    
    
        def clear(self):
            for item in self.cart.item_set.all():
                item.delete()
    

and models.py:

    
    
    class Cart(models.Model):
        creation_date = models.DateTimeField(verbose_name=_('creation date'))
        checked_out = models.BooleanField(default=False, verbose_name=_('checked out'))
    
        class Meta:
            verbose_name = _('cart')
            verbose_name_plural = _('carts')
            ordering = ('-creation_date',)
    
        def __unicode__(self):
            return unicode(self.creation_date)
    
    class ItemManager(models.Manager):
        def get(self, *args, **kwargs):
            if 'equipment' in kwargs:
                kwargs['content_type'] = ContentType.objects.get_for_model(type(kwargs['equipment']))
                kwargs['object_id'] = kwargs['equipment'].pk
                del(kwargs['equipment'])
            return super(ItemManager, self).get(*args, **kwargs)
    
    class Item(models.Model):
        cart = models.ForeignKey(Cart, verbose_name=_('cart'))
        content_type = models.ForeignKey(ContentType)
        object_id = models.PositiveIntegerField()
    
        objects = ItemManager()
    
        class Meta:
            verbose_name = _('item')
            verbose_name_plural = _('items')
            ordering = ('cart',)
    
        def __unicode__(self):
            return u'%d units of %s' % (self.quantity, self.equipment.__class__.__name__)
    
        # product
        def get_product(self):
            return self.content_type.get_object_for_this_type(pk=self.object_id)
    
        def set_product(self, equipment):
            self.content_type = ContentType.objects.get_for_model(type(equipment))
            self.object_id = equipment.pk
    

When trying to go the view displaying current cart, I got this problem:

> RecursionError at /calbase/cart/ maximum recursion depth exceeded in
> comparison

and basically it repeats calling the following :

    
    
    cart = Cart(request, creation_date=datetime.datetime.now()) 
    cart = self.new(request) 
    cart = Cart(request, creation_date=datetime.datetime.now()) 
    cart = self.new(request) 
    

.....

I am aware that this is because I am calling _init_ when doing cart =
Cart(...) and this again go back to cart = self.new(request) and tried several
ways to fix this, in vain. Could somebody help me?

Environment:

    
    
    Request Method: GET
    Request URL: http://127.0.0.1:8000/calbase/cart/
    
    Django Version: 1.10
    Python Version: 3.5.2
    Installed Applications:
    ['calbase.apps.CalbaseConfig',
     'django.contrib.admin',
     'django.contrib.auth',
     'django.contrib.contenttypes',
     'django.contrib.sessions',
     'django.contrib.messages',
     'django.contrib.staticfiles',
     'haystack',
     'whoosh']
    Installed Middleware:
    ['django.middleware.security.SecurityMiddleware',
     'django.contrib.sessions.middleware.SessionMiddleware',
     'django.middleware.common.CommonMiddleware',
     'django.middleware.csrf.CsrfViewMiddleware',
     'django.contrib.auth.middleware.AuthenticationMiddleware',
     'django.contrib.messages.middleware.MessageMiddleware',
     'django.middleware.clickjacking.XFrameOptionsMiddleware']
    

Traceback:

    
    
    File "C:\Users\hansong.li\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\core\handlers\exception.py" in inner
      39.             response = get_response(request)
    
    File "C:\Users\hansong.li\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\core\handlers\base.py" in _get_response
      187.                 response = self.process_exception_by_middleware(e, request)
    
    File "C:\Users\hansong.li\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\core\handlers\base.py" in _get_response
      185.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)
    
    File "C:\Users\hansong.li\Documents\GitHub\equipCal\calbase\views.py" in get_cart
      72.     return render_to_response('cart.html', dict(cart=Cart(request)))
    
    File "C:\Users\hansong.li\Documents\GitHub\equipCal\calbase\cart.py" in __init__
      22.             cart = self.new(request)
    
    File "C:\Users\hansong.li\Documents\GitHub\equipCal\calbase\cart.py" in __init__
      22.             cart = self.new(request)
    
    File "C:\Users\hansong.li\Documents\GitHub\equipCal\calbase\cart.py" in new
      30.         cart = Cart(request, creation_date=datetime.datetime.now())
    
    Exception Type: RecursionError at /calbase/cart/
    Exception Value: maximum recursion depth exceeded in comparison
    


Answer: You have two separate classes called Cart. Rename one of ,them.

