I know in php I could just use $_GET['key1']['key2'] to retrieve GET data that is sent in the form of an array but is that something possible in Python as I just receive a string and it's not recognized as an array/list.
I use flask/werkzeug if that matters.
The deep parsing of argument names is unique for PHP AFAIK.
If you need just a simple list, just pass several parameters with the same name and use request.args.getlist(<paramname>) (documentation).
Otherwise you have to parse the query string yourself.