My discord python bot's shop cause it to freeze

Question

I have been making a discord economy bot and it has a shop. When I try and buy an item from my shop in the bot, the bot does not respond with anything and I won't recognise any other commands. The bot also gives me an error in the command prompt. This error is in the picture. Any help given is great.

https://i.stack.imgur.com/SsBwA.png

My code:

mainshop = [{"name":"Airbus A320","price":400,"description":"test description"}]

@client.command()
async def shop(ctx):
    em = discord.Embed(title = "Dealership")

    for item in mainshop:
        name = item["name"]
        price = item["price"]
        desc = item["description"]
        em.add_field(name = name, value = f"${price} | {desc}")

    await ctx.send(embed =em)


@client.command()
async def buy(ctx,item,amount = 1):
    await open_account(ctx.author)

    res = await buy_this(ctx.author,item,amount)

    if not res[0]:
        if res[1]==1:
            await ctx.send("That item does not exisit!")
            return
        if res [1]==2:
            await ctx.send(f"You do not have enough money!")
            return


    await ctx.send(f"you just bought {amount} {item}")

async def buy_this(user,item_name,amount):
    item_name - item_name.lower()
    name_ = None
    for item in mainshop:
        name = item["name"].lower()
        if name == item_name:
            name_ = name_
            price = item["price"]
            break

    if name_ ==None:
        return [False,1]

    cost = price*amount

    users = await get_bank_data()

    bal = await update_bank(user)

    if bal[0]<cost:
        return [False,2]


    try:
        index = 0
        t = None
        for thing in users[str(user.id)]["bag"]:
            n = thing["item"]
            if n == item_name:
                old_amt = thing["amount"]
                new_amt = old_amt + amount
                users[str(user.id)]["bag"][index]["amount"] = new_amt
                t = 1
                break
            index+=1
        if t == None:
            obj = {"item":item_name , "amount" : amount}
            users[str(user.id)]["bag"].append(obj)
    except:
        obj = {"item":item_name , "amount" : amount}
        users[str(user.id)]["bag"] =[obj]

    with open("bank.json","w") as f:
        json.dump(users,f)

    await update_bank(user,cost*-1,"Wallet")

    return [True,"Worked"]```

Answer 1

you have a typing mistake in buy_this function.

item_name - item_name.lower()

You need to put '=' instead of '-', like this:

item_name = item_name.lower()