谁是小偷

# a说我不是小偷；b说c是小偷；c说小偷肯定是d；d说c胡说！

def find_thief():
    human = ['a', 'b', 'c', 'd']
    for thief in human:
        truth = (thief != 'a') + (thief == 'c') + (thief == 'd') + (thief != 'd')
        if truth == 3:
            return thief