dice.py

#!/usr/bin/env python3
# -*- coding: UTF-8 -*-

"""
A module for dice, dice rolls, and dice arithmetic.
"""

import sys
import re
from types import ModuleType


class DiceModule(ModuleType):
    dice_pattern = re.compile(r'^d([1-9][0-9]*)$')

    class Die:
        __slots__ = 'sides',
        def __init__(self, sides) -> None:
            self.sides = sides

        def roll(self) -> int:
            from random import randint
            return randint(1, self.sides)

        def __rmul__(self, other) -> int:
            if isinstance(other, int):
                return other * self.roll()
            return NotImplemented

    def __getattr__(self, attr):
        m = self.dice_pattern.match(attr)
        if not m:
            return super().__getattr__(attr)
        return self.Die(int(m.group(1)))


sys.modules[__name__] = DiceModule(__name__, __doc__)

dice_test.py

#!/usr/bin/env python3
# -*- coding: UTF-8 -*-

import pytest


def test_import():
    from dice import Die, d20
    assert isinstance(d20, Die)
    assert d20.sides == 20


def test_roll():
    from dice import d20
    for _ in range(20):
        assert 1 <= d20.roll() <= 20


def test_roll_multiple():
    from dice import d6
    for _ in range(36):
        assert 2 <= 2 * d6 <= 12


def test_arithmetic():
    from dice import d6
    for _ in range(36):
        assert 2 + 5 <= 2 * d6 + 5 <= 36 + 5


def test_bonkers():
    from dice import d34321

    with pytest.raises(ImportError):
        from dice import does_not_exist

    with pytest.raises(ImportError):
        from dice import d007