set_solver.py

from itertools import combinations
from collections import namedtuple

Card = namedtuple("Card", ["color", "shape", "shade", "number"])

cards = [
    Card("red", "diamond", "hollow", 1),
    Card("green", "squiggle", "solid", 3),
    Card("red", "oval", "striped", 3),
    Card("red", "oval", "hollow", 2),
    Card("purple", "oval", "hollow", 1),
    Card("purple", "diamond", "solid", 1),
    Card("purple", "squiggle", "solid", 3),
    Card("red", "diamond", "solid", 3),
    Card("green", "oval", "hollow", 3),
    Card("red", "diamond", "hollow", 2),
    Card("green", "oval", "striped", 3),
    Card("red", "oval", "hollow", 1),
]

match = None
for potential in combinations(cards, 3):
    if len(set(card.color for card in potential)) in (1, 3) and \
       len(set(card.shape for card in potential)) in (1, 3) and \
       len(set(card.shade for card in potential)) in (1, 3) and \
       len(set(card.number for card in potential)) in (1, 3):
        match = potential
        break

if not match:
    print("No set found")
else:
    print("Set found: ")
    for card in match:
        print(card)