Two Ways to Implement a Feature Nobody Asked For

import typing

import data_types  # New module!

R = typing.TypeVar('R')
E = typing.TypeVar('E')

class Result(data_types.Data, typing.Generic[R, E]):

    class Constructors(data_types.Constructors):
        # Constraints are required at runtime, but may not be enforced
        Ok = R,
        Err = E,

---

import typing

import data_types  # New module!

R = typing.TypeVar('R')
E = typing.TypeVar('E')

class Result(data_types.Data, typing.Generic[R, E]):

    class Constructors(data_types.Constructors):
        # Constraints may not exist, but mypy should fail if they don't
        Ok: R,
        Err: E,