<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def to_iso639_1(key):
 """Find ISO 639-1 code for language specified by key. u'sv' u'en' """

    item = find(whatever=key)
    if not item:
        raise NonExistentLanguageError('Language does not exist.')
    return item[u'iso639_1']