Added simple web page, routes are in a separate file

flaskapp/app.py

@@ -2,32 +2,38 @@
 
 import os
 import secrets
-from pathlib import Path
 
 from flask import Flask
 
+from . import routes
+from . import errors
+
 
 def create_app() -> Flask:
     """Flask app factory function"""
 
-    root = Path('..')
-    static = str(root / 'static')
-    tmpl = str(root / 'templates')
-
+    # Create an app object
     app = Flask(
         __name__,
-        static_folder=static,
-        template_folder=tmpl,
+        static_folder='../static',
+        template_folder='../templates',
         instance_relative_config=True,
     )
+    # Get the token from environment
+    # or generate it using secrets
     app.config['SECRET_KEY'] = os.getenv(
         'SECRET_KEY',
         secrets.token_hex(32),
     )
 
+    # Create instance/ directory
     try:
         os.makedirs(app.instance_path)
     except OSError:
         pass
 
+    # Add routes
+    routes.add_routes(app)
+    errors.add_routes(app)
+
     return app

flaskapp/errors.py

@@ -0,0 +1,48 @@
+"""Flask app error handlers"""
+
+from pathlib import Path
+
+from flask import Flask
+from flask import render_template
+
+# Add other HTTP error codes here
+CODES = [404, 500]
+
+
+def add_routes(app: Flask) -> None:
+    """Add all error handlers
+
+    Args:
+        app (Flask): Flask application
+    """
+
+    tmpl_dir = app.template_folder
+    if tmpl_dir is None:
+        return
+
+    tmpl = Path(__file__).parent / tmpl_dir
+
+    for code in CODES:
+        add_handler(app, tmpl, code)
+
+
+def add_handler(
+        app: Flask,
+        tmpl: Path,
+        code: int) -> None:
+    """Add Flask app error handler.
+    Only for internal use
+
+    Args:
+        app (Flask): Flask application
+        file (str): Template filename
+        code (int): Error code
+    """
+
+    file = f'{code}.html'
+
+    if (tmpl / file).exists():
+
+        @app.errorhandler(code)
+        def handler(_e):
+            return render_template(file), code

flaskapp/routes.py

@@ -0,0 +1,16 @@
+"""Main Flask app routes"""
+
+from flask import Flask
+from flask import render_template
+
+
+def add_routes(app: Flask) -> None:
+    """Add main routes
+
+    Args:
+        app (Flask): Flask application
+    """
+
+    @app.route('/')
+    def index():
+        return render_template('index.html')