You could let the users download a file, with their progress in it (to save), and add a load function (to load the text in the file).
at python you can make it with the modul "repl.it" i don't have use this module ever but i have see it in codes from other peoples. as fare as i know it asks you about your replt.it name and password.
You will need to setup a database, if you're familiar with JSON format of data storage then use mongodb otherwise you can also use some or the other distribution of SQL. You won't be able to save data on files in repl.it