automatically add furigana

from anki import hooks
def onLoadNote(n):
    global mecab
    if not mecab:
        return
    src = None
    dst = None
    # japanese model?
    if not isJapaneseNoteType(n.model()['name']):
        return
    # have src and dst fields?
    fields = mw.col.models.fieldNames(n.model())
    for field in srcFields:
        if field in fields:
            src = field
            break
    for field in dstFields:
        if field in fields:
            dst = field
            break
    if not src or not dst:
        return
    # dst field exists?
    if dst not in n:
        return
    # dst field already filled?
    if n[dst]:
        return
    # grab source text
    srcTxt = mw.col.media.strip(n[src])
    if not srcTxt:
        return
    # update field
    try:
        n[dst] = mecab.reading(srcTxt)
    except Exception as e:
        mecab = None
        raise
hooks.note_will_flush.append(onLoadNote)