DEH 9000 is a "programmer's Dehacked". It provides a Python API for generating Dehacked patches that also makes the standard contents of the tables that Dehacked modifies available to the user.
DEH 9000 uses Doom's internal variable and type names so that if you've ever experimented with the Doom source code things should seem familiar. If you ever wanted to be able to just hack around with Doom's internal tables and automatically generate a Dehacked patch of your changes then you'll like DEH 9000.
See the guide for some documentation on how to use DEH 9000.
The Python API for editing WAD files is called OMGIFOL, a reference to a quote from 2001: A Space Odyssey. The computer in that story is called HAL 9000, so DEH 9000 is continuing the Python Doom/Space Odyssey theme. Also, the most powerful weapon in Doom is the BFG 9000, so it also fits as a name that suggests "most powerful Dehacked".