This still does not allow python to change the value under the memory location passed by reference?

Ideally, a special Python ByRef type should be constructed to hold the value until function exits, then the caller should check if Python updated the value in the ByRef instance, and update the value pointed by reference accordingly.

Perhaps, but your scenario is not the one in #1355 . This PR at least prevents crashes.

Since you can't override Python assignment operator, this fix is fundamentally incompatible with the proper solution with ByRef, so will have to be replaced by 3.0.0, otherwise it will be a breaking change.

Even if we don't implement updating the value right now, to avoid making breaking changes later the value has to be wrapped into some Python object instance.

E.g. in the linked issue the handler code should be

def handleEventData(data):
    print("=== event invoked. data: {} ===".format(data.Value)) # NOTE .Value

When Python calls a .NET method with ref arguments, it returns a tuple of out/ref parameters, and if there's a return value it is the first in the tuple. See methodbinder.cs and stackoverflow. Therefore the "proper solution" is for handleEventData to return a tuple of out/ref parameter values. No special ByRef type is needed.

Good point. Still for forward compatibility we must at least check Python returns a tuple of the correct size, or better yet actually implement the marshaling of updated variables back to the event.

So is this supposed to be released with 2.5.2?