highspy: Passing user_callback_data to setCallback raises exception

[few]

The following code raises an exception (at least on the latest branch):

h = highspy.Highs()

def callback(callback_type, message, data_out, data_in, user_callback_data):
    pass

user_callback_data = {}
h.setCallback(callback, user_callback_data)

TypeError: setCallback(): incompatible function arguments. The following argument types are supported:
    1. (self: highspy._core._Highs, arg0: Callable[[int, str, HighsCallbackDataOut, HighsCallbackDataIn, capsule], None], arg1: capsule) -> highspy._core.HighsStatus

Invoked with: <highspy.highs.Highs object at 0x7f9b12ffa160>, <function callback at 0x7f9b132b7d90>, {}

Passing None as user_callback_data works.

[jajhall]

This is done so that users can pass data required in a callback. It works fine in C++ (and C, I think). I've got no idea how to make it work in Python

[few]

I found a workaround:

import highspy

h = highspy.Highs()
h.readModel("30n20b8.mps")
h.setOptionValue("time_limit", 90)

class CallbackManager:
    mip_solution = None

    def callback(self, callback_type, message, data_out, data_in, user_callback_data):
        self.mip_solution = data_out.mip_solution

callback_manager = CallbackManager()
h.setCallback(callback_manager.callback, None)
h.startCallback(highspy.cb.HighsCallbackType.kCallbackMipImprovingSolution)
h.run()
h.stopCallback(highspy.cb.HighsCallbackType.kCallbackMipImprovingSolution)

print("best solution so far:", callback_manager.mip_solution)

This way one can store arbitrary data in the CallbackManager object. Maybe user_callback_data is not needed in highspy?

[jajhall]

Closed by #1942