$ sides = int(web.form(sides=6).sides)

Roll of a $(sides)-sided die: **$random.randint(1, sides)**

<form>
<input name=sides type=hidden value=$sides>
<button>Reroll</button>
</form>

<form>
<label>Sides: <input name=sides type=text></label>
<div><button>Roll</button></div>
</form>