48 — Shop — an inventory store

Guide 33 saved a list and 31 saved records. A store grows that idea one step: a dict of items (each with price and stock) plus a money balance, all in shop.json.

#Steps

1. The shop is one JSON object with two parts: an items dict mapping a name to {"price": N, "stock": N}, plus a money balance:

   {
     "items": {
       "apple": {"price": 3, "stock": 10},
       "banana": {"price": 5, "stock": 5},
       "cherry": {"price": 2, "stock": 0}
     },
     "money": 20
   }
   

   copyrun it →

2. The whole store. Save shop.nme next to shop.json. use file latest loads json_load/json_save, and os.path.exists starts a fresh shop:

   # shop.nme — a small store kept in a JSON file.
   # Run: nme r shop
   # Type list, buy, sell, or quit.
   
   use file latest
   import os
   
   if os.path.exists("shop.json"):
       data = json_load("shop.json")
   else:
       data = {"items": {}, "money": 20}
   
   while True:
       show f"Money: {data['money']}"
       show "Commands: list, buy, sell, quit"
       ask command, "? "
       if command == "list":
           for name in data["items"]:
               item = data["items"][name]
               show f"{name}: {item['price']} each, {item['stock']} in stock"
       elif command == "buy" or command == "sell":
           ask name, "Item? "
           if name in data["items"]:
               item = data["items"][name]
               if command == "buy":
                   if item["stock"] > 0:
                       item["stock"] = item["stock"] - 1
                       data["money"] = data["money"] - item["price"]
                       show f"Bought {name}"
                       json_save("shop.json", data)
                   else:
                       show "Out of stock"
               else:
                   item["stock"] = item["stock"] + 1
                   data["money"] = data["money"] + item["price"]
                   show f"Sold {name}"
                   json_save("shop.json", data)
           else:
               show "No such item"
       elif command == "quit":
           show "Bye!"
           break
       else:
           show "Unknown command"
   

   copyrun it →

   list walks the dict with for name in data["items"]:; buy and sell share one branch via or (guide 09). Buy pays the price and drops stock; sell refunds and adds; json_save writes it back, so the store survives between runs.

3. Run it and feed the commands through a pipe. buy apple pays 3 and drops stock to 9, sell apple refunds it:

   printf 'list\nbuy\napple\nsell\napple\nquit\n' | nme r shop
   

   copy

   Money: 20
   Commands: list, buy, sell, quit
   ? apple: 3 each, 10 in stock
   banana: 5 each, 5 in stock
   cherry: 2 each, 0 in stock
   Money: 20
   Commands: list, buy, sell, quit
   ? Item? Bought apple
   Money: 17
   Commands: list, buy, sell, quit
   ? Item? Sold apple
   Money: 20
   Commands: list, buy, sell, quit
   ? Bye!
   

   copy

#Try it yourself

Add a restock <name> <count> command that adds to an item's stock, or an add <name> <price> command that inserts a new item and saves it.

#What you learned

• A store is a dict of item dicts plus a money balance, all saved as JSON.
• for name in data["items"]: lists a dict's keys and reads each item.
• buy/sell change the balance and the stock, then json_save persists.
• A quit command with break ends the while True: menu.