old_contents: """
  Prerequisites
  
      pip3 install spotipy Flask Flask-Session
  
      export SPOTIPY_CLIENT_ID=client_id_here
      export SPOTIPY_CLIENT_SECRET=client_secret_here
      // on Windows, use `SET` instead of `export`
  
  Run app.py
  
      python3 -m flask run --port=8080
  """
  
  import os
  from flask import Flask, session, request, redirect
  from flask_session import Session
  import spotipy
  
  app = Flask(__name__)
  app.config['SECRET_KEY'] = os.urandom(64)
  app.config['SESSION_TYPE'] = 'filesystem'
  
  Session(app)
  
  auth_manager = spotipy.oauth2.SpotifyOAuth()
  spotify = spotipy.Spotify(auth_manager=auth_manager)
  
  
  @app.route('/')
  def index():
      if request.args.get("code"):
          session['token_info'] = auth_manager.get_access_token(request.args["code"])
          return redirect('/')
  
      if not session.get('token_info'):
          auth_url = auth_manager.get_authorize_url()
          return f'<h2><a href="{auth_url}">Sign in</a></h2>'
  
      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>'
  
  
  @app.route('/sign_out')
  def sign_out():
      session.clear()
      return redirect('/')
  
  
  @app.route('/playlists')
  def playlists():
      if not session.get('token_info'):
          return redirect('/')
      else:
          return spotify.current_user_playlists()
new_contents: """
  Prerequisites
  
      pip3 install spotipy Flask Flask-Session
  
      export SPOTIPY_CLIENT_ID=client_id_here
      export SPOTIPY_CLIENT_SECRET=client_secret_here
      export SPOTIPY_REDIRECT_URI='http://127.0.0.1:8080' // added to your [app settings](https://developer.spotify.com/dashboard/applications)
      // on Windows, use `SET` instead of `export`
  
  Run app.py
  
      python3 -m flask run --port=8080
  """
  
  import os
  from flask import Flask, session, request, redirect
  from flask_session import Session
  import spotipy
  
  app = Flask(__name__)
  app.config['SECRET_KEY'] = os.urandom(64)
  app.config['SESSION_TYPE'] = 'filesystem'
  
  Session(app)
  
  auth_manager = spotipy.oauth2.SpotifyOAuth()
  spotify = spotipy.Spotify(auth_manager=auth_manager)
  
  
  @app.route('/')
  def index():
      if request.args.get("code"):
          session['token_info'] = auth_manager.get_access_token(request.args["code"])
          return redirect('/')
  
      if not session.get('token_info'):
          auth_url = auth_manager.get_authorize_url()
          return f'<h2><a href="{auth_url}">Sign in</a></h2>'
  
      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>'
  
  
  @app.route('/sign_out')
  def sign_out():
      session.clear()
      return redirect('/')
  
  
  @app.route('/playlists')
  def playlists():
      if not session.get('token_info'):
          return redirect('/')
      else:
          return spotify.current_user_playlists()
  
subject: Add redirect_uri (#529)