A few updates to the example app (#540)

* No username needed + can be used by multiple users

* cleanup

* Remove caches when signing out

* Persist token only once

* Always show auth page

* Add one scope..

* Add a second scope and also a view which utilizes a scope.

* Add a __main__ clause example.

* Include further documentation.

* Move utility function higher in document.

* Add threading to application run call in __main__.

* Add (or reinstate–I thought it had been there) the "me" view.

* Add notes about SPOTIPY_REDIRECT_URI and using alternate port.

And specify that it should be the address that the App runs over.

* Whitespace only.

* Here is an example of importing credentials.

* Delete session_cache file on logout so new user can Authorize.

* Not going to use at this point.

* Update the "me" route method to use new approach to auth.

* Update app.py

Co-authored-by: Stephane Bruckert <contact@stephanebruckert.com>
Co-authored-by: Stephane Bruckert <stephane.bruckert@gmail.com>

examples/app.py

@@ -7,12 +7,20 @@ Prerequisites
     export SPOTIPY_CLIENT_ID=client_id_here
     export SPOTIPY_CLIENT_SECRET=client_secret_here
     export SPOTIPY_REDIRECT_URI='http://127.0.0.1:8080' // must contain a port
+    // SPOTIPY_REDIRECT_URI must be added to your [app settings](https://developer.spotify.com/dashboard/applications)
+    OPTIONAL
+    // in development environment for debug output
+    export FLASK_ENV=development
+    // so that you can invoke the app outside of the file's directory include
+    export FLASK_APP=/path/to/spotipy/examples/app.py
  
     // on Windows, use `SET` instead of `export`
 
 Run app.py
 
     python3 -m flask run --port=8080
+    NOTE: If receiving "port already in use" error, try other ports: 5000, 8090, 8888, etc...
+        (will need to be updated in your Spotify app and SPOTIPY_REDIRECT_URI variable)
 """
 
 import os
@@ -31,6 +39,8 @@ caches_folder = './.spotify_caches/'
 if not os.path.exists(caches_folder):
     os.makedirs(caches_folder)
 
+def session_cache_path():
+    return caches_folder + session.get('uuid')
 
 @app.route('/')
 def index():
@@ -38,7 +48,10 @@ def index():
         # Step 1. Visitor is unknown, give random ID
         session['uuid'] = str(uuid.uuid4())
 
-    auth_manager = spotipy.oauth2.SpotifyOAuth(cache_path=session_cache_path(), show_dialog=True)
+    auth_manager = spotipy.oauth2.SpotifyOAuth(scope='user-read-currently-playing playlist-modify-private',
+                                                cache_path=session_cache_path(), 
+                                                show_dialog=True)
+
     if request.args.get("code"):
         # Step 3. Being redirected from Spotify auth page
         auth_manager.get_access_token(request.args.get("code"))
@@ -53,20 +66,26 @@ def index():
     spotify = spotipy.Spotify(auth_manager=auth_manager)
     return f'<h2>Hi {spotify.me()["display_name"]}, ' \
            f'<small><a href="/sign_out">[sign out]<a/></small></h2>' \
-           f'<a href="/playlists">my playlists</a>'
+           f'<a href="/playlists">my playlists</a> | ' \
+           f'<a href="/currently_playing">currently playing</a> | ' \
+		   f'<a href="/current_user">me</a>' \
 
 
 @app.route('/sign_out')
 def sign_out():
     os.remove(session_cache_path())
     session.clear()
+    try:
+        # Remove the CACHE file (.cache-test) so that a new user can authorize.
+        os.remove(session_cache_path())
+    except OSError as e:
+        print ("Error: %s - %s." % (e.filename, e.strerror))
     return redirect('/')
 
 
 @app.route('/playlists')
 def playlists():
     auth_manager = spotipy.oauth2.SpotifyOAuth(cache_path=session_cache_path())
-
     if not auth_manager.get_cached_token():
         return redirect('/')
 
@@ -74,5 +93,31 @@ def playlists():
     return spotify.current_user_playlists()
 
 
-def session_cache_path():
+@app.route('/currently_playing')
-    return caches_folder + session.get('uuid')
+def currently_playing():
+    auth_manager = spotipy.oauth2.SpotifyOAuth(cache_path=session_cache_path())
+    if not auth_manager.get_cached_token():
+        return redirect('/')
+    spotify = spotipy.Spotify(auth_manager=auth_manager)
+    track = spotify.current_user_playing_track()
+    if not track is None:
+        return track
+    return "No track currently playing."
+
+
+@app.route('/current_user')
+def current_user():
+    auth_manager = spotipy.oauth2.SpotifyOAuth(cache_path=session_cache_path())
+    if not auth_manager.get_cached_token():
+        return redirect('/')
+    spotify = spotipy.Spotify(auth_manager=auth_manager)
+    return spotify.current_user()
+
+
+'''
+Following lines allow application to be run more conveniently with
+`python app.py` (Make sure you're using python3)
+(Also includes directive to leverage pythons threading capacity.)
+'''
+if __name__ == '__main__':
+	app.run(threaded=True, port=int(os.environ.get("PORT", 8080)))