def _add_expansion_to_acronym_dict(acronym, expansion, level, dictionary):
    """Add an acronym to the dictionary.

    Takes care of avoiding duplicates and keeping the expansion marked with
    the best score.
    """
    if len(acronym) >= len(expansion) or acronym in expansion:
        return

    for punctuation in re.findall("\W", expansion):
        # The expansion contains non-basic punctuation. It is probable
        # that it is invalid. Discard it.
        if punctuation not in (",", " ", "-"):
            return False

    if acronym in dictionary:
        add = True
        for stored_expansion, stored_level in dictionary[acronym]:
            if _equivalent_expansions(stored_expansion, expansion):
                if level < stored_level:
                    dictionary[acronym].remove(
                        (stored_expansion, stored_level))
                    break
                else:
                    add = False
        if add:
            dictionary[acronym].append((expansion, level))
            return True
    else:
        dictionary.setdefault(acronym, []).append((expansion, level))
        return True

    return False
Add an acronym to the dictionary.

    Takes care of avoiding duplicates and keeping the expansion marked with
    the best score.