Django: error when entering the cart page, but how to fix it?

Question

Python

When adding an item to the cart, an error occurs in cart.py: *KeyError: 'quantity'*.

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)

views.py

from django.shortcuts import redirect, get_object_or_404, render
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})

def cart_detail(request):
    cart = Cart(request)
    for item in cart:
        item['update_quantity_form'] = CartAddProductForm(
            initial={'quantity': item['quantity'], 'update': True})
    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):
        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):
        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):
        product_id = str(product.id)
        if product_id in self.cart:
            del self.cart[product_id]
            self.save()

    def __iter__(self):
        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):
        return sum(item['quantity'] for item in self.cart.values())

    def get_total_price(self):
        return sum(Decimal(item['price']) * item['quantity'] for item in
                self.cart.values())

    def clear(self):
        del self.session[settings.CART_SESSION_ID]
        self.session.modified = True

The error itself:

File "C:\Users\user\AppData\Local\Programs\Python\Python310\lib\site-packages\django\core\handlers\exception.py", line 47, in inner
    response = get_response(request)
  File "C:\Users\user\AppData\Local\Programs\Python\Python310\lib\site-packages\django\core\handlers\base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Users\user\Desktop\Django\myshop\cart\views.py", line 31, in cart_detail
    for item in cart:
  File "C:\Users\user\Desktop\Django\myshop\cart\cart.py", line 48, in __iter__
    item['total_price'] = item['price'] * item['quantity']
KeyError: 'quantity'

Answer 1

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

The values() method returns a list of all values ​​available in the given dictionary.
You are trying to access the values ​​of dictionaries like a dictionary