The documentation says
walk_set(self, photoset_id, per_page=50, ...)
source code
Other arguments can be passed, as documented in the flickr.photosets.getPhotos API call in the Flickr API documentation, except for page because all pages will be returned eventually.
If I just want 20 results, how can I do that? Otherwise, its just keep on running and getting the data
Thank you
As described on the getPhotos, you can do:
walk_set(self, photoset_id, per_page=20, page=1)