friends_cls.py

class Friends(set):
    def __init__(self, connections=set()):
        super().__init__(map(frozenset, connections))

    def add(self, connection):
        if connection in self:
            return False

        super().add(frozenset(connection))
        
        return True

    def remove(self, connection):
        if connection in self:
            super().remove(connection)
            return True
        
        return False

    def names(self):
        return set().union(*self)

    def connected(self, name):
        return Friends(filter({name}.issubset, self)).names() - {name}



if __name__ == '__main__':
    #These "asserts" using only for self-checking and not necessary for auto-testing
    letter_friends = Friends(({"a", "b"}, {"b", "c"}, {"c", "a"}, {"a", "c"}))
    digit_friends = Friends([{"1", "2"}, {"3", "1"}])
    assert letter_friends.add({"c", "d"}) is True, "Add"
    assert letter_friends.add({"c", "d"}) is False, "Add again"
    assert letter_friends.remove({"c", "d"}) is True, "Remove"
    assert digit_friends.remove({"c", "d"}) is False, "Remove non exists"
    assert letter_friends.names() == {"a", "b", "c"}, "Names"
    assert letter_friends.connected("d") == set(), "Non connected name"
    assert letter_friends.connected("a") == {"b", "c"}, "Connected name"