Why doesn't Django add to cart work?

Question

Django

Error when adding product to cart:
Page not found (404)
Request Method: GET
Request URL: 127.0.0.1:8000/cart
Raised by: shop.views.product_list
No Category matches the given query.

I transfer from one application to the second.
Shop app:
urls.py

from django.urls import path, include
from . import views

app_name='shop'

urlpatterns=[
    path('',views.product_list, name='product_list'),
    path('menu/',views.menu, name='menu'),
    path('delivery/',views.delivery, name='delivery'),
    path('news/',views.news, name='news'),
    path('news/<int:id>/<slug:slug>/',views.news_detail, name='news_detail'),
    path('<str:category_slug>/',views.product_list, name='product_list_by_category'),
    path('<int:id>/<slug:slug>/',views.product_detail,name='product_detail'),
]

views.py

from django.shortcuts import render, HttpResponse, get_object_or_404
from .models import Category, Product, Articles
from django.core.paginator import Paginator, EmptyPage, PageNotAnInteger

# Create your views here.

def index(request):
    return render(request, 'shop/product/index.html')

def product_list(request,category_slug=None):
    category = None
    categories= Category.objects.all()
    products = Product.objects.filter(available=True)
    if category_slug:
        category = get_object_or_404(Category, slug=category_slug)
        products = products.filter(category=category)
    paginator = Paginator(products, 1)
    page = request.GET.get('page')
    try:
        posts = paginator.page(page)
    except PageNotAnInteger:
        posts = paginator.page(1)
    except EmptyPage:
        posts = paginator.page(paginator.num_pages)


    return render(request,'shop/product/index.html',{'category': category,'categories': categories,'products': products, 'page': page,'posts': posts})

def menu(request):
    categories= Category.objects.all()
    return render(request,'shop/product/menu.html',{'categories': categories})

def delivery(request):
    categories= Category.objects.all()
    return render(request,'shop/product/delivery.html',{'categories': categories})

def news(request):
    categories= Category.objects.all()
    articles= Articles.objects.all()
    return render(request,'shop/product/news.html',{'articles': articles,'categories': categories})

def news_detail(request,id,slug):
    categories= Category.objects.all()
    news = get_object_or_404(Articles,id=id,slug=slug)
    return render(request, 'shop/product/news_detail.html', {'article': news,'categories': categories})


def product_detail(request,id,slug):
    categories= Category.objects.all()
    product = get_object_or_404(Product,id=id,slug=slug,available=True)
    return render(request, 'shop/product/detail.html', {'product': product,'categories': categories})

Submission Form

<form action="{% url 'cart:cart_add' product.id %}" method="post">
                    {{ cart_product_form }}
                    {% csrf_token %}
                    <button class="main-content_block-item_btn" type="submit">
                        В корзину
                    </button>
                </form>

cart application:
urls.py

from django.urls import path, include
from . import views

app_name='cart'

urlpatterns = [
    path('add/<int:product_id>/', views.cart_add, name='cart_add'),
    path('remove/<int:product_id>/', views.cart_remove, name='cart_remove'),
    path('', views.cart_detail, name='cart_detail'),
]

views.py

from django.shortcuts import render, redirect, get_object_or_404
from django.views.decorators.http import require_POST
from shop.models import Product
from .cart import Cart
from .forms import CartAddProductForm


@require_POST
def cart_add(request, product_id):
    cart = Cart(request)
    product = get_object_or_404(Product, id=product_id)
    form = CartAddProductForm(request.POST)
    if form.is_valid():
        cd = form.cleaned_data
        cart.add(product=product,
                 quantity=cd['quantity'],
                 update_quantity=cd['update'])
    return redirect('cart:cart_detail')

def cart_remove(request, product_id):
    cart = Cart(request)
    product = get_object_or_404(Product, id=product_id)
    cart.remove(product)
    return redirect('cart:cart_detail')

def cart_detail(request):
    cart = Cart(request)
    return render(request, 'cart/detail.html', {'cart': cart})

cart.py

from decimal import Decimal
from django.conf import settings
from shop.models import Product


class Cart(object):

    def __init__(self, request):
        """
        Инициализируем корзину
        """
        self.session = request.session
        cart = self.session.get(settings.CART_SESSION_ID)
        if not cart:
            # save an empty cart in the session
            cart = self.session[settings.CART_SESSION_ID] = {}
        self.cart = cart
    
    def add(self, product, quantity=1, update_quantity=False):
        """
        Добавить продукт в корзину или обновить его количество.
        """
        product_id = str(product.id)
        if product_id not in self.cart:
            self.cart[product_id] = {'quantity': 0,
                                    'price': str(product.price)}
        if update_quantity:
            self.cart[product_id]['quantity'] = quantity
        else:
            self.cart[product_id]['quantity'] += quantity
        self.save()

    def save(self):
        # Обновление сессии cart
        self.session[settings.CART_SESSION_ID] = self.cart
        # Отметить сеанс как "измененный", чтобы убедиться, что он сохранен
        self.session.modified = True
    
    def remove(self, product):
        """
        Удаление товара из корзины.
        """
        product_id = str(product.id)
        if product_id in self.cart:
            del self.cart[product_id]
            self.save()


    def __iter__(self):
        """
        Перебор элементов в корзине и получение продуктов из базы данных.
        """
        product_ids = self.cart.keys()
        # получение объектов product и добавление их в корзину
        products = Product.objects.filter(id__in=product_ids)
        for product in products:
            self.cart[str(product.id)]['product'] = product

        for item in self.cart.values():
            item['price'] = Decimal(item['price'])
            item['total_price'] = item['price'] * item['quantity']
            yield item

    def __len__(self):
        """
        Подсчет всех товаров в корзине.
        """
        return sum(item['quantity'] for item in self.cart.values())

    def get_total_price(self):
        """
        Подсчет стоимости товаров в корзине.
        """
        return sum(Decimal(item['price']) * item['quantity'] for item in
                self.cart.values())

    
    def clear(self):
        # удаление корзины из сессии
        del self.session[settings.CART_SESSION_ID]
        self.session.modified = True

forms.py

from django import forms

PRODUCT_QUANTITY_CHOICES = [(i, str(i)) for i in range(1, 21)]


class CartAddProductForm(forms.Form):
    quantity = forms.TypedChoiceField(choices=PRODUCT_QUANTITY_CHOICES, coerce=int)
    update = forms.BooleanField(required=False, initial=False, widget=forms.HiddenInput)

Answer 1

https://docs.djangoproject.com/en/3.0/topics/http/...
add to main urlspath('cart/', include('cart.urls')),