Feature Request: Improve generic DPT handling

Part 1:

It seems that some DPT parsing is implemented in remote values (e.g. DPT 251.600). This makes these DPTs unavailable for generic transcoding via transcoder_by_dpt or transcode_by_value_type.

Is there any deeper reason, that those DPTs are not part of the standard DPT handling? Is it, because they consist out of multiple values (in the RGBW case)?

If yes, followup question: is there a possibility to restructure the code to generically (via DPT main and sub number) get transcoders for those DPTs as well?

Part 2:

Some DPT implementations (like DPTDate seem to lack dpt_main_number and dpt_sub_number definitions from what I see.

Is that on purpose, am I missing something or is it just not implemented yet?

I'm happy to provide PRs to improve the handling of this, once it's clear, how it should be done.

Hi 👋!

Is it, because they consist out of multiple values (in the RGBW case)?

Yes, exactly. The transcoder lookup was initially implemented for HA sensor entity value types. So it should only return compatible (numeric or string) DPTs.

If yes, followup question: is there a possibility to restructure the code to generically (via DPT main and sub number) get transcoders for those DPTs as well?

DPTNumeric was implemented at a later point - this could solve at least a part of this issue

xknx/xknx/dpt/dpt.py

Line 177 in 92b80c2

class DPTNumeric(DPTBase):

Some DPT implementations lack dpt_main_number and dpt_sub_number definitions (...) Is that on purpose

Yes, see above. DPT subclasses without main/sub number were excluded from lookup.

I have made an attempts previously to support multi-value DPTs. Unfortunately I never finished those. See #1276 and #1277
The idea was to have a properly typed data structures (for internal use eg. for HA integration) that are also easily json compatible (for HA automations, frontend websockets etc.) and of course adhere KNX Specifications and are easy to use (default values etc.)
If you want to take one of these up, be my guest. Feel free to contact me on Discord or here if you want to chat about it or have any questions.