I am trying to create a function that enhances a type with another type. Below is a simple example…

def combine(name, A, B): # -> CombinationType[A, B]:
   return type(name, (A, B), {})

class Hello:
   def hello(self):
      return "hello"

class Goodbye:
   def goodbye(self):
      return "goodbye"

both = combine("Both", Hello, Goodbye)

b = both()
b.hello()     ■ Instance of 'Both' has no 'hello' member
b.goodbye()     ■ Instance of 'Both' has no 'goodbye' member

mypy doesn’t like the resulting Both type, for obvious reasons (no return typehint on combine).

Is there any way to represent something like this in python? You can assume the latest-and-greatest 3.12.x or 3.13.x

My actual use case is a bit more involved, but conceptually the same: I want to take in a dataclass type and create a new type that adds the ctypes.Structure base and appropriate _fields_ values.

from ctypes import Structure, c_uint16
from dataclasses import dataclass

def structureify(datacls): # -> CombinationType[T, Structure]:
   return type(datacls.__name__, (datacls, Structure), {"_fields_" = ...})

@structify
@dataclass
class Test:
   test_member: c_uint16

And ideally I would like to be able to typehint/… on the resulting class (e.g. Test.from_buffer(...) from Structure, and Test.test_member, …).