Move i3 container to next empty workspace, and follow

i3-move-to-empty.py

#!/usr/bin/python3

import json, subprocess

output = subprocess.check_output(['i3-msg', '-t', 'get_workspaces'])
workspaces = json.loads(output)

next_num = next(i for i in range(1, 100) if not [ws for ws in workspaces if ws['num'] == i])

subprocess.call(['i3-msg', f'move container to workspace number {next_num}; workspace {next_num}'])