Minor improvements

run.sh

@@ -3,4 +3,4 @@ docker run -it --rm \
     -h testlabhost \
     -p 8009:8000 \
     -e PORT=8000 \
-    $TAG:latest
\ No newline at end of file
+    $TAG:latest

src/app.py

@@ -80,7 +80,7 @@ app.add_routes([
     web.get("/page3", test3_handler),
 ])
 
+ENV_PORT:str = os.environ.get('PORT')
+port_number = int(ENV_PORT) if ENV_PORT is not None and ENV_PORT.isdigit() else 8000
 
-
-port_number = int(os.environ.get('PORT')) if os.environ.get('PORT').isdigit() else 8000
 web.run_app(app, port=port_number)