[xxyzz]

I move the code to a file:

#!/usr/bin/env python3

from calibre.library import db
from calibre.utils.logging import default_log
from calibre.ebooks.mobi.reader.mobi6 import MobiReader

lib_db = db('~/Calibre Library').new_api
alice_id = 0
for book_id in lib_db.all_book_ids():
    mi = lib_db.get_metadata(book_id)
    if mi.get('title') == "Alice's Adventures in Wonderland":
        alice_id = book_id
        break

book_path = lib_db.format_abspath(alice_id, 'MOBI')
mobiReader = MobiReader(book_path, default_log)
mobiReader.extract_text()

Use calibre-debug to run this code should reproduce the error.