def add_folder_download_callback(callback):
session.folder_download_callbacks.append(callback)<EOL>
Pass a function to be called when an folder has finished downloading,
which happens after all of its items and recursive children folders
have downloaded.
This can be used for performing notifications of download progress or
calling additional API functions.

:param callback: A function that takes four arguments. The first argument
    is the communicator object of the current pydas context, the second is
    the currently active API token, the third is the dict of folder info,
    the fourth argument is the local download path of the folder.
:type callback: (Communicator, string, dict, string) -> unknown