"Alfred filters results" gives empty list

[valrus]

I'm working on a script to play music using MPD. I want to list available albums and have Alfred filter them rather than doing the filtering myself in a script filter. But when I check the "Alfred filters results" check box, the result is an empty list regardless of what I type:

 

If, on the other hand, I uncheck that box, I get a list of albums as expected, but I can't type to filter them:

 

Here's my code, in Python. It's really not very complicated:

from __future__ import unicode_literals
from __future__ import print_function

import json
import os
import subprocess
import sys

MUSIC_DIR = '/Users/Shared/iTunes/iTunes Media/Music'
FIND_CMD = [
    '/usr/local/bin/mpc', 'list', 'album'
]


def make_item(album_name):
    return dict(
        title=album_name,
        uid=album_name,
        valid=True,
        arg=json.dumps({'album': album_name}),
        icon='icon.png',
        autocomplete=album_name,
    )


def main():
    print(json.dumps({
        'items': [
            make_item(item)
            for item in subprocess.check_output(FIND_CMD).decode('utf-8').split('\n')
            if item.strip()
        ]
    }))


if __name__ == '__main__':
    sys.exit(main())

 

Can anyone tell me what I might be doing wrong?

Edited March 8, 2017 by valrus
Moving images to better locations inline

[valrus]

I figured it out. The problem is that I was triggering the script filter with a hotkey, and I had incorrectly chosen "Pass through to workflow" rather than "Show Alfred" as the Action.

 

I'm not totally clear on why this matters; since my script filter doesn't actually use its arguments when "Alfred filters results" is checked, why should it matter if I pass something in from the hotkey? If someone can explain that, it might help my understanding. But my main problem is solved.