pyimgui window constraints -- problems with python callbacks in C code

constrained_window.py

# pyimgui version:
#   https://github.com/lubieowoce/pyimgui/commit/62bd989bf3621df125f68d0e07423668a68bf9c9

def limit_aspect_ratio_2(position, current_size, desired_size) -> 'Tuple[float, float]':
    print('limit_aspect_ratio_2(_, current_size={}, desired_size={})'.format(current_size, desired_size))
    w, h = desired_size
    return (h*2, h)


def draw():
    # Different ways of passing a callback to `imgui.unsafe_set_next_window_size_constraints(...)`

    # 1. ok
    imgui.unsafe_set_next_window_size_constraints(
        min_width=10, min_height=10,
        max_width=500, max_height=500,
        callback = limit_aspect_ratio_2,
    )

    # # 2. CRASH - should be equivalent to 1, but crashes -
    # # the lambda is garbage collected before `imgui.begin(...)`
    # imgui.unsafe_set_next_window_size_constraints(
    #   min_width=10, min_height=10,
    #   max_width=500, max_height=500,
    #   callback = lambda pos, cs, ds: limit_aspect_ratio_2(pos, cs, ds),
    # )

    # # 3a. ok - we keep a reference to the lambda, so it doesn't get collected
    # cb = lambda pos, cs, ds: limit_aspect_ratio_2(pos, cs, ds)
    # imgui.unsafe_set_next_window_size_constraints(
    #   min_width=10, min_height=10,
    #   max_width=500, max_height=500,
    #   callback = cb,
    # )

    # # 3b. ok - we keep a reference to the lambda, so it doesn't get collected
    # # (`unsafe_set_next_window_size_constraints` returns its callback for testing purposes)
    # callback_keepalive = imgui.unsafe_set_next_window_size_constraints(
    #   min_width=10, min_height=10,
    #   max_width=500, max_height=500,
    #   callback = lambda pos, cs, ds: limit_aspect_ratio_2(pos, cs, ds),
    # )

    print('begin drawing `constrained`')

    imgui.begin("constrained")
    imgui.text("window size: {}".format(imgui.get_window_size()))
    imgui.end()

    print('end drawing `constrained`\n')