def lag_interessegrupper(personers_interesse):
    interesse_ordbok = {}

    for person in personers_interesse:
        interesse = personers_interesse[person]

        if interesse not in interesse_ordbok:
            interesse_ordbok[interesse] = [person]
        else:
            interesse_ordbok[interesse].append(person) 

    return interesse_ordbok

print(lag_interessegrupper({"Per":"Mat", "Palle":"Film", "Espen":"Mat"}))