def METHOD_NAME(self):
    """Create _by_slug dict mapping slugs to list of lemma and all wordforms"""
    self._by_slug = defaultdict(list)
    for entry in self._full_dictionary:
        if "slug" in entry:
            assert "formOf" not in entry
            self._by_slug[entry["slug"]].append(entry)
        elif "formOf" in entry:
            assert "slug" not in entry
            self._by_slug[entry["formOf"]].append(entry)
        else:
            raise AssertionError("Entry must contain either formOf or slug")