Available environment variables from downloader.py

I’m trying to send pushover notification by setting downloader.py to start script when donwload is complete.
The script itself is working well. That send a notification with the message “Download completed” to my phone.
But I couldn’t figure out how to send ‘downloaded file name’ as the text message.

I’m really noob about coding and also about english.
so I don’t know I could ask you what I want to ask.
but If there is someone who can understand what I’m asking, please leave a comment.
Thanks