I built a tiny dice-dungeon game in Python in one evening

Everyone says "build projects" but nobody tells you the project can be dumb and small. So here is my dumb small project: a text game where you walk through five rooms, a goblin is in every room, and everything is decided by dice. I wrote it in one evening with nothing except plain Python, and I learned more from it than from a month of watching tutorials.

The idea

The game has three things:

1. You have HP (health) and gold.
2. In each room a goblin appears and you choose fight or run.
3. Dice decide what happens. After five rooms, if you're alive, you win.

That's the whole spec. I wrote it on the back of my chemistry rough copy before touching the keyboard, and that mattered. When I start coding without writing the spec I usually end up building something else.

The code

import random

def roll(sides=6):
    return random.randint(1, sides)

def encounter(hp, gold):
    print("A goblin jumps out!")
    while True:
        choice = input("fight or run? ").strip().lower()
        if choice in ("fight", "run"):
            break
        print("type fight or run, bro")

    if choice == "run":
        if roll() >= 4:
            print("you escaped!")
        else:
            hp -= 2
            print("tripped. -2 hp")
        return hp, gold

    mine, theirs = roll(), roll()
    print(f"you rolled {mine}, goblin rolled {theirs}")
    if mine >= theirs:
        gold += 3
        print("goblin down. +3 gold")
    else:
        hp -= 3
        print("ouch. -3 hp")
    return hp, gold

def main():
    hp, gold = 10, 0
    for room in range(1, 6):
        print(f"\n--- Room {room} | HP {hp} | Gold {gold} ---")
        hp, gold = encounter(hp, gold)
        if hp <= 0:
            print("you died with", gold, "gold")
            return
    print("\nYou escaped the dungeon with", gold, "gold!")

main()

If you copy this and run it, it works. It took me an hour to get here because of the first three bugs, which I'll talk about in a second.

The bugs, in the order they humiliated me

Bug 1: the infinite loop. My first version of the fight or run question didn't have the break, so after a valid answer it just asked again forever. I sat there typing "fight" like a fool and wondering why the goblin never appeared. while True: loops need an exit. Write the exit first, then the loop body.

Bug 2: forgetting .strip().lower(). My friend typed Fight with a capital F and a trailing space and the game said it was an invalid choice. Players do weird things. Whatever the user types, clean it first.

Bug 3: I changed hp inside the function and nothing happened outside it. This is the classic. Numbers are passed by value, so changing hp inside encounter doesn't touch the hp in main. The fix is what you see above: return hp, gold and then hp, gold = encounter(hp, gold). I understood functions properly only after this one.

The part I didn't expect: the maths

After it worked I played ten times and kept dying. Was the game unfair or was I unlucky? So I did the probability, which is basically class 11 stuff.

When both roll a six-sided die and I win on ties, the number of favourable outcomes is: 6 ties plus 15 where mine is higher, so 21 out of 36.

$P(\text{win a fight}) = \frac{21}{36} = \frac{7}{12} \approx 0.58$

So each fight, I gain 3 gold with probability $\frac{7}{12}$ and lose 3 HP with probability $\frac{5}{12}$. The expected change in HP per fight is

$E[\Delta \text{HP}] = -3 \times \frac{5}{12} = -1.25$

Over five rooms that's about $-6.25$ HP on average, out of 10 HP to start. So most runs are survivable but the variance is big, which is why it felt so deadly.

And running? You escape if you roll 4 or more, which is $\frac{3}{6} = \frac{1}{2}$. Otherwise you lose 2 HP, so the expected loss is $-1$ HP per run. Running costs less health than fighting, but gives zero gold. So the game quietly became a risk vs reward choice, and I hadn't even designed it that way. I just typed numbers.

What I changed after the maths

I made the goblins get tougher in later rooms (they roll a 6-sided die plus the room number divided by two, rounded down) and I added a potion room. Then I noticed the potion room made the early game too easy, so I moved it. This tweak-test-tweak cycle is exactly what real game designers do and it was weirdly addictive.

Things I want to add next, in order:

• A shop between rooms where gold buys a re-roll
• Saving the high score to a text file
• Different monsters with different dice (a d4 bat, a d8 troll)

What I'd tell a beginner

• Write the spec first, even if it's silly. Ten lines in plain English.
• Make it run early. My first version only printed the room number. Then I added the goblin. Then the dice. Never try to write the whole thing in one go.
• Print everything while debugging. print(hp) is not a crime.
• Pick a game, not a calculator. I was bored of "make a todo app" and I never would have finished it. Wanting to see the goblin die kept me going.

I ran it for my little cousin and she asked if the goblin could have a name. So now there's a goblin_names list with seven names and one of them is "Sharmaji". Don't ask.