Quilt combination generator - ensure each 3x3 block contains a unique permutation of 5 coloured pieces

quilt.py

import random

# FIXME fill in numbers of each unique piece here

tiles = {
    "a": 10,
    "b": 10,
    "c": 10,
    "d": 10,
    "e": 10,
    "f": 10,
    "g": 10,
    "h": 10,
    "i": 10,
    "j": 10,
    "k": 10,
    "l": 10,
    "m": 10,
    "n": 10,
    "o": 10,
}

# then:
#
# population = "".join(x * tiles[x] for x in tiles)
#
# else generate random example instead - population of 140

letters = "abcdefghijklmno"

population = ""

while len(population) < 140:
    population += random.choice(letters)

population = "".join(sorted(population))

squares = []

while len(squares) < 25:
    square = set(random.choices(population, k=5))
    if len(square) < 5:
        # reject non unique
        continue
    if square in squares:
        # reject duplicate
        continue
    # keep it
    squares.append(square)

    # remove the letters from population
    for s in square:
        i = population.index(s)
        population = population[:i] + population[i + 1 :]

# passed

assert len(population) == 15

for j, square in enumerate(squares):
    print(j + 1, "".join(sorted(square)))