I don't think Python has anything to do with anything. The editor is written in Godot's GDScript and dernc.exe was written in C.
There could be some very obscure reason why dernc.exe isn't working for you. What version of Windows are you using? One idea is to try using the dernc.exe executable by itself to see if that works. In command line (Run -> cmd) you use it very simply like so:
"C:\directory\dernc.exe" "C:\directory\TMAPA000.DAT"
But for now, to get the editor up and working, you simply need some decompressed TMAPA files. The latest alpha of KeeperFX supplies them decompressed already.
https://keeperklan.com/threads/7239-KeeperFX-Test-builds-for-version-0-4-9
https://keeperfx-loobinex.keeperklan.com/alphabuilds/
Since you have 0.4.8 you'd have to install keeperfx_0_4_9_alpha_2215.7z then fx_alpha_2696_from_2215.zip, which as of writing this post is the latest.
If there's a reason you don't want to install the latest KeeperFX, you can simply copy the tmapa files from fx_alpha_2696_from_2215.zip into your DK's /data/ directory, replacing the old ones.
By the way these files only contain texture map tilesets, nothing more. I just remembered you can also tell if a tmapa file is decompressed by whether it's 544KB or not.