Print a customizable app name and other improvements

README.md

@@ -0,0 +1,4 @@
+# python-sample
+The simplest posible webapp in flask. 
+This app responds to GET requests at / printing  'Hello World from {APP_NAME}!', where APP_NAME is optional and it is read from an environment variable.
+It's compatible with python 3.8+.  

app.py

@@ -5,9 +5,10 @@
 
 @app.route('/')
 def hello():
-    return 'Hello World!'
+    app_name = os.environ.get('APP_NAME', '[set APP_NAME env var]')
+    return 'Hello World from {}!'.format(app_name)
 
 if __name__ == '__main__':
     # Bind to PORT if defined, otherwise default to 5000.
     port = int(os.environ.get('PORT', 5000))
-    app.run(host='0.0.0.0', port=port)
+    app.run(host='0.0.0.0', port=port)

requirements.txt

@@ -1,4 +1,6 @@
-Flask==0.9
-Jinja2==2.6
-Werkzeug==0.8.3
-wsgiref==0.1.2
+click==7.1.2
+Flask==1.1.2
+itsdangerous==1.1.0
+Jinja2==2.11.3
+MarkupSafe==1.1.1
+Werkzeug==1.0.1