defmodule Supervisor.PyOperatorManager do
  use Supervisor

  def start_link(_) do
    Supervisor.start_link(__MODULE__, [], name: __MODULE__)
  end

  @impl true
  def init(_) do
    Process.flag(:trap_exit, true)

    children = [
      :poolboy.child_spec(:py_pool,
        name: {:local, :py_pool},
        worker_module: Server.PyOperator,
        size: 10,
        max_overflow: 5
      )
    ]

    Supervisor.init(children, strategy: :one_for_one)
  end

  def launch(data \\ [], py_module, py_lambda) do
    :poolboy.transaction(:py_pool, fn pid ->
      GenServer.call(pid, {data, py_module, py_lambda}, 30_000)
    end)
  end
end

defmodule Server.PyOperator do
  use GenServer
  use Export.Python

  def start_link(_) do
    GenServer.start_link(__MODULE__, %{})
  end

  @impl true
  def init(state) do
    Process.flag(:trap_exit, true)

    priv_path = Path.join(:code.priv_dir(:arbit), "python")
    {:ok, py} = Python.start_link(python_path: priv_path)
    {:ok, Map.put(state, :py, py)}
  end

  @impl true
  def handle_call({data, py_module, py_lambda}, _from, %{py: py} = state) do
    results = Python.call(py, py_module, py_lambda, [data])

    results
    |> IO.inspect(label: "#{__MODULE__} - line 23")

    {:reply, results, state}
  end

  @impl true
  def terminate(_reason, %{py: py}) do
    Python.stop(py)
    :ok
  end
end

#foo.py
import simplejson as json
from erlport.erlterms import Atom
from heavy_processes import some_heavy_process
from some_lib.errors import (AuthenticationError, PermissionDenied, ArgumentsRequired, BadRequest, 
                        BadResponse, NullResponse, NotSupported, NetworkError, DDoSProtection,
                        RateLimitExceeded, OnMaintenance, InvalidNonce, RequestTimeout)


def transmit_report(success_status, report, id, category, misc):
    success_status_as_bytes = bytes(success_status, encoding='utf8')
    full_report = report | {
        'id': id, 'category': category, 'misc?': misc}
    full_report_json = json.dumps(full_report)

    return (Atom(success_status_as_bytes), (full_report_json))


def do_stuff(params_json):
    params = json.loads(params_json)

    id = params["id"]
    category = params["category"]
    misc = params["misc"]

    arg1 = params["arg1"]
    arg2 = params["arg2"]
    arg3 = params["arg3"]
    arg4 = params["arg4"]
    arg5 = params["arg5"]

    try:
        report = some_heavy_process(
            arg1, arg2, arg3, arg4, arg5)

    except (AuthenticationError, PermissionDenied, ArgumentsRequired, BadRequest, BadResponse,
            NullResponse, NotSupported, NetworkError, DDoSProtection,
            RateLimitExceeded, OnMaintenance, InvalidNonce, RequestTimeout) as error:

        transmit_report(
            'error', {'error': str(error)}, id, category, misc)
    except Exception as crash_report:
        transmit_report('error', {'error': str(
            crash_report)}, id, category, misc)
    else:
        transmit_report(
            'ok', report, id, category, misc)


def main(params_json):
    do_stuff(params_json)


if __name__ == '__main__':
    main(params_json)

Issue:
Calling Supervisor.PyOperatorManager.launch(params_json, "foo", "main") only returns :undefined instead of the tuple from transmit_report.

How is this issue resolved?