routes_absolute.py

class ApiRoot:
    Base = "/api"
    Frontend = "/ui"

class Users:
    inner_base = ApiRoot.Base + "/users"

    Register = inner_base + "/register"

    ByName = lambda name: ApiRoot.Users.inner_base + f"/{name}" 

fastapi_app = FastAPI()

@fastapi_app.post(Users.Register)
async def users_register():
    return None

@fastapi_app.get(Users.ByName("{name}"))
async def users_get_by_name(name: str):
    return name