Flask send_file is sending old file instead of newest

send_file has a caching timeout that you are not configuring. It will send the same file that has been cached unless you tell it not to cache the file like so:

send_file('./tmp/{}'.format(basename), as_attachment=True, cache_timeout=0)

See the following references for more information:

http://flask.pocoo.org/docs/1.0/api/#flask.send_file

http://flask.pocoo.org/docs/1.0/api/#flask.Flask.get_send_file_max_age

http://flask.pocoo.org/docs/1.0/config/#SEND_FILE_MAX_AGE_DEFAULT