update_anki_notes.py

import re
from anki import Collection
from anki.media import MediaManager 

regex = re.compile(u"\[sound:[^\]]+]")
col = Collection("<collection-path>.anki2")
mm = MediaManager(col, None)
ids = col.findCards("deck:<deck-name>")
for id in ids:
    card = col.getCard(id)
    note = card.note()
    hanzi = note.fields[1]
    filepath = u"zh/{}.mp3".format(hanzi)
    filepath = mm.addFile(filepath)
    note.fields[2] = re.sub(regex, "", note.fields[2])
    note.fields[2] += "[sound:" + filepath + "]" 
    note.flush()
mm.close()
col.close()