I can upload a File with flask by following Uploading Files:
tag is marked with enctype=multipart/form-data and an file = request.files['file']
change it to
file = request.files['file[]']
the issue here is that flask's app.config isn't relative to itself, it's absolute. so when you put:
UPLOAD_FOLDER = './uploads'
flask doesn't find this directory and returns a 500 error.
if you changed it to:
UPLOAD_FOLDER = '/tmp'
and then uploaded your file and navigated to the /tmp/ directory you would see it.
you will need to edit your path to the proper directory for the file to be uploaded properly.