Solution

app/customer.py

@@ -31,10 +31,12 @@ def calculate_travel_cost(
         return round(l_per_km * distance * fuel_price * 2, 2)
 
     def calculate_cart_cost(self, shop: Shop) -> int | float:
-        cart_cost = 0
-        for item in self.product_cart:
-            cart_cost += self.product_cart[item] * shop.products[item]
-        return cart_cost
+        if shop.products:
+            cart_cost = 0
+            for item in self.product_cart:
+                cart_cost += self.product_cart[item] * shop.products[item]
+            return cart_cost
+        return 0
 
     def calculate_total_cost(
         self,

app/main.py

@@ -13,10 +13,10 @@ def shop_trip() -> None:
     for customer in customers:
         print(f"{customer.name} has {customer.money} dollars")
 
-        cheapest_shop = [None, 0]
+        cheapest_shop = [None, float("inf")]
         for shop in shops:
             total_cost = customer.calculate_total_cost(fuel_price, shop)
-            if total_cost < cheapest_shop[1] or cheapest_shop[1] == 0:
+            if total_cost < cheapest_shop[1]:
                 cheapest_shop[0] = shop
                 cheapest_shop[1] = total_cost
             print(f"{customer.name}'s trip to "