test or code is wrong?

I would like to give some feedback about ...

From: https://checkio.org/mission/friends/solve/

class Friends: def init(self, connections): print(connections); self.connections = connections;

def add(self, connection):
    if connection in self.connections:
        return False
    else:
        self.connections = list(self.connections);
        self.connections.append(connection);
        return True

def remove(self, connection):
    deleted = False;
    for elem in self.connections:
        if str(elem) == str(connection):
            print(type(self.connections));
            print("test1:");
            print(self.connections);
            self.connections.remove(elem);
            print("test2:");
            print(self.connections);
            deleted = True;
    return deleted

def names(self):
    result = []
    for elem in self.connections:
        for x in elem:
            result.append(x)
    result = set(result);
    print("result:");
    print(result);
    return result

def connected(self, name):
    new_list = [];
    new_list2 = [];
    print("name: " + name);
    check = False;
    for elem in self.connections:
        for item in elem:
            item_buffer = item;
            print("item: " + item);
            if check == True:
                new_list2.append(item);
                check = False;
            #item_buffer.append(item);
            if item == name:
                print("same!");
                #new_list2.append(item_buffer);
                check = True;
            new_list.append(item);
        item_buffer = ();
    print("new_list:");
    print(new_list);
    print("new_list2:");
    print(new_list2);
    print(set(new_list2));
    return set(new_list2);

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

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Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:47.0) Gecko/20100101 Firefox/47.0

Please check if it is your test or my code, I have no idea why the "remove()" cannot be used?

All the best

AttributeError: 'tuple' object has no attribute 'remove', remove, 22, , 7 f = Friends(({"nikola", "sophia"}, {"stephen", "robot"}, {"sophia", "pilot"})) f.remove({"stephen", "robot"}) f.names()