ElectronのFlaskが動作しない

ElectronのFlaskが動作せずエラーになってしまいます。

以下のサイトを参考にしました。
https://qiita.com/goto_y/items/6cabe72da415755b29b5

Python
1app.py
2
3from __future__ import print_function
4import time
5from flask import Flask, render_template
6
7app = Flask(__name__)
8
9@app.route("/")
10def hello():
11    return render_template("index.html")
12
13if __name__ == "__main__":
14    print('on hello')
15    app.run(host="127.0.0.1", port=5000)
16

json
1package.json
2
3{
4  "name": "sample_app",
5  "version": "1.0.0",
6  "description": "",
7  "main": "index.js",
8  "scripts": {
9    "test": "echo \"Error: no test specified\" && exit 1"
10  },
11  "keywords": [],
12  "author": "",
13  "license": "ISC",
14  "devDependencies": {
15    "electron": "^6.0.2"
16  },
17  "dependencies": {
18    "python-shell": "^1.0.8",
19    "request": "^2.88.0",
20    "request-promise": "^4.2.4"
21  }
22}
23

javascript
1index.js
2
3// Electron側の初期設定
4const {PythonShell} = require('python-shell');
5const electron = require('electron');
6const app = electron.app;
7const BrowserWindow = electron.BrowserWindow;
8let mainWindow;
9
10// アプリを閉じた時にquit
11app.on('window-all-closed', function() {
12  app.quit();
13});
14
15// アプリ起動後の処理
16app.on('ready', function() {
17  PythonShell.run('./app.py', null, function (err, result) {  // exe:'./resources/app/app.py'    edit: './app.py'
18    if (err) throw err;
19    console.log(result);
20  });
21  const rq = require('request-promise');
22  const mainAddr = 'http://localhost:5000';
23
24  const openWindow = function() {
25    mainWindow = new BrowserWindow({width: 400, height: 300 });
26    mainWindow.loadURL(mainAddr);
27
28    // 開発ツールを有効化
29    // mainWindow.webContents.openDevTools();
30
31    // 終了処理
32    mainWindow.on('closed', function() {
33
34      // キャッシュを削除
35      electron.session.defaultSession.clearCache(() => {})
36      mainWindow = null;
37    });
38  };
39
40  const startUp = function() {
41    rq(mainAddr)
42      .then(function(htmlString) {
43        console.log('server started');
44        openWindow();
45      })
46      .catch(function(err) {
47        startUp();
48      });
49  };
50
51  startUp();
52});

html
1index.html
2
3<!DOCTYPE html>
4<html lang="ja">
5<head>
6    <meta charset="UTF-8">
7    <title>Title</title>
8    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css" integrity="sha384-9gVQ4dYFwwWSjIDZnLEWnxCjeSWFphJiwGPXr1jddIhOegiu1FwO5qRGvFXOdJZ4" crossorigin="anonymous">
9</head>
10<body>
11<div class="container">
12    <h1>Hello, World!</h1>
13    <button class="btn btn-primary">button</button>
14    <p id="text">text</p>
15</div>
16</body>
17</html>