optimization_progress_changed event Leave feedback

Occurs when the progress of the optimization operation has changed.

node_event_hub.optimization_progress_changed += handler    # subscribe handler(sender, args)
node_event_hub.optimization_progress_changed -= handler    # remove the last subscription of handler
node_event_hub.optimization_progress_changed.clear()       # remove every handler added from Python

The handler runs on the thread that raises the event, which can be an engine worker thread. An exception it raises there is printed to stderr and ignored; on the calling thread it reaches the engine, as in .NET.

• class NodeEventHub