ImportError：尝试在烧瓶中没有已知父包的情况下进行相对导入

文件夹结构

.
├── myapp
│   ├── api
│   │   └── routes.py
│   ├── app.py
│   |
│   └── site
│       └── routes.py

app.py位于api文件夹和站点文件夹之外的myapp文件夹中

api / routes.py

from flask import Blueprint
api = Blueprint('api',__name__,url_prefix='api')

@api.route('/userlist/')
def user():
  return { 1: 'user1', 2:'user2'}

site / routes.py

from flask import Blueprint

site = Blueprint('site',__name__)

@site.route('/')
def index():
  return 'Welcome to the Home page'

app.py

from flask import Flask
from .site.routes import site
from .api.routes import api

def create_app():
  app = Flask(__name__)
  app.register_blueprint(api)
  app.register_blueprint(site)
  return app

在终端中使用“ flask run”命令运行flask应用程序时出现此错误

Traceback (most recent call last):
 File "app.py", line 2, in <module>
  from .site.routes import site
ImportError: attempted relative import with no known parent package

我不明白如何解决这个问题。提前致谢 ：）