我們正在嘗試運(yùn)行 aflask db migrate并flask db upgrade引發(fā)以下錯(cuò)誤：Usage: flask db upgrade [OPTIONS] [REVISION]Error: The file/path provided (C) does not appear to exist.  Please verify the path            is correct.  If app is not on PYTHONPATH, ensure the extension is .py我們已將應(yīng)用程序的目錄添加到PYTHONPATH環(huán)境變量中，但仍然出現(xiàn)錯(cuò)誤。任何幫助，將不勝感激。下面是我們的__init__.py代碼。我們錯(cuò)過(guò)了什么嗎？import loggingfrom flask import Flaskfrom flask_appbuilder import SQLA, AppBuilder""" Logging configuration"""logging.basicConfig(format='%(asctime)s:%(levelname)s:%(name)s:%(message)s')logging.getLogger().setLevel(logging.DEBUG)app = Flask(__name__)app.config.from_object('config')db = SQLA(app)appbuilder = AppBuilder(app, db.session)migrate.init_app(app, db)"""from sqlalchemy.engine import Enginefrom sqlalchemy import event#Only include this for SQLLite constraints@event.listens_for(Engine, "connect")def set_sqlite_pragma(dbapi_connection, connection_record):    # Will force sqllite contraint foreign keys    cursor = dbapi_connection.cursor()    cursor.execute("PRAGMA foreign_keys=ON")    cursor.close()"""    from app import views