Python - RPG game

#!/usr/bin/env python3

# global variable
inv = ["Steel Sword" , "Shield" , "Health Potion" , "Strange Bun" , "Gold"]

def room_shop(previous_room):
    global inv # to have access to external variable `inv` without passing it as function's argument

    shop = ["Health Potion" , "Boots" , "Strange Bun" , "Mysterious Crystal"]

    # room description
    print("--------------------------------------------------------")
    print("Welcome to the shop!")
    print("You can buy something or exit.")
    print("--------------------------------------------------------")

    # command loop
    while True:
        print("Below is the list of items we have in stock.")
        print(shop)

        command = input("So, what can I get for you today, traveller? ")
        command = command.strip().lower().split(1)

        print('DEBUG:', command)

        if command[0] in ("exit", "quit", "bye"):
            print("Good Bye! And come back later.")
            return previous_room
        elif command in ("inv", "inventory", "show inventory"):
            print("This is your current inventory")
            print(inv)
        elif command in ("items",):
            print("Below is the list of items we have in stock.")
            print(shop)
        elif command == "health potion":
            print("That'll be 10G, thank you!")
            inv.append("Health Potion")
            print(inv)
        elif command == "boots":
            print("That'll be 40G, thank you!")
            inv.append("Boots")
            print(inv)
        elif command == "strange bun":
            print("That'll be 5G, thank you!")
            inv.append("Strange Bun")
            print(inv)
        elif command == "mysterious crystal":
            print("That.. I don't remember having this.. Oh well, make it 100G")
            inv.append("Mysterious Crystal")
            print(inv)
        else:
            print("I clearly don't sell that, mate.")

def room_main(previous_room):
    global inv # to have access to external variable `inv` without passing it as function's argument

    # room description
    print("--------------------------------------------------------")
    print("You are in the main room.")
    print("You can go forward, left, right, backword, shop or exit.")
    print("--------------------------------------------------------")

    # command loop
    while True:
        print("This is your current inventory")
        print(inv)

        command = input("Which commandion would you like to travel? ")
        command = command.strip().lower()

        if command in ("exit", "quit", "bye"):
            print("Bye!")
            break # exist loop
            return
        elif command == "forward":
            print("You found a Health Potion!")
            inv.append("Health Potion")
            print(inv)
        elif command == "right":
            choice = input("You encounter an enemy! What do you do? ")
            choice = choice.strip().lower()
            if choice == "steel sword":
                print("You slayed a monster! You gain 34XP and lose 5HP")
            else:
                print("You used the wrong item and the monster killed you. The end.")
        elif command == "left":
            choice = input("Somebody shoots an arrow at you! What do you do? ")
            choice = choice.strip().lower()
            if choice == "shield":
                print("You successfuly defended against the arrows, you gain 50XP")
        elif command == "backwards":
            choice = input("You walk into a trap, and lose 30HP. What do you do? ")
            if choice == "health potion":
                print("You use the Health Potion and gain 20HP.")
        elif command == "shop":
            return 'shop'

# --- start ---

rooms = {
    'main': room_main,
    'shop': room_shop,
}

previous_room = ''
current_room = 'main'

while True:
    function = rooms[current_room]
    next_room = function(previous_room)
    if next_room is None:
        break # exit `while` loop and exit game
    previous_room = current_room
    current_room = next_room