pip install dmenu

file_handler.py

#!/usr/bin/python
from dmenu import dmenu
import sys
import os

browser = 'xdg-open %s'
choices = {
        'Open in thunar' : 'thunar %s',
        'Open in firefox':'firefox %s',
        }


if len(sys.argv) <2:
    print("Call this with file url as argument.")
    sys.exit()


if sys.argv[1][0:7] == 'file://':
    # The url passed in to url-handler is a file:// url.
    cmd = dmenu.show(choices.keys(), prompt='Choose application')
    full_command = choices[cmd] %  sys.argv[1]
else:
    full_command = browser % sys.argv[1]

print(os.system(full_command))