title: Flask send_from_directory returns 404 for certain filenames
body: <p>let me show you an example:</p>
  <p>This is the folder that I want to send the files from:</p>
  <pre><code>app.config['DOWNLOAD_FOLDER'] = os.path.join(app.root_path, 'downloads')
  </code></pre>
  <p>I return the files like this from the route:</p>
  <pre><code>return send_from_directory(app.config['DOWNLOAD_FOLDER'], song_title,as_attachment=True)
  </code></pre>
  <p>I get 404 for certain files such as:</p>
  <blockquote>
  <p>Baby Shark Dance _ Most Viewed Video on YouTube _ PINKFONG Songs for Children.mp3</p>
  </blockquote>
  <blockquote>
  <p>'E.T.' - Katy Perry (Rock Cover by First To Eleven).mp3</p>
  </blockquote>
  <p>It works perfectly fine for these:</p>
  <blockquote>
  <p>The Witcher Soundtrack - Toss A Coin To Your Witcher Lyrics.mp3</p>
  </blockquote>
  <blockquote>
  <p>Yung Felix - Loco ft. Poke &amp; Dopebwoy.mp3</p>
  </blockquote>
  <p>I tried to place the song_title in a formatted raw string like this:</p>
  <pre><code>return send_from_directory(app.config['DOWNLOAD_FOLDER'], r&quot;{}&quot;.format(song_title), as_attachment=True)
  </code></pre>
  <p>It didn't work.</p>
  <p>Here is the entire route function:</p>
  <pre><code>    @app.route('/home', methods=['POST', 'GET'])
  def home():
  
      if request.method == 'POST':
          
          song_name = request.form.get('songname')
          song_url, song_title = get_youtube_url_from_name(song_name)
          song_title = song_title + '.mp3'
          download_mp3_from_url(song_url)
          return send_from_directory(app.config['DOWNLOAD_FOLDER'], secure_filename(song_title),
                               as_attachment=True)
          # flash(song_title + ' has been successfully downloaded!')
          # return redirect(url_for('home'))
  
      return render_template('home.html')
  </code></pre>
  <p>Thank you for your time.</p>