`on_position_event` callback receives each event twice

[Dia Kharrat]

Bug Report

The on_position_event callback in a strategy is being called with duplicate events. It receives each PositionEvent twice. This is using backtesting. I haven't tried testing it live mode, so not sure if this happens there too or not. On the other hand, the on_event callback receives the event once, so this seems isolated to the on_position_event callback.

Expected Behavior

The on_position_event callback should receive an event once.

Actual Behavior

The on_position_event callback receives each event twice, resulting in the strategy receiving duplicate events.

Steps to Reproduce the Problem

1. Create a test strategy that submits a market order and add a print statement in the on_position_event callback that prints the event.id. You'll notice that the callback receives each event twice.

Specifications

• OS platform: Ubuntu
• Python version: 3.11
• nautilus_trader version: Develop branch (commit a29de8a)

[Chris Sellers]

Hi @dkharrat

This is the intended design and explained here in the docs.

You only need to handle the event in either the specific position event handler, the general on_position_event handler, or the on_event handler - at your choice.

This also applies to order events too, see the event handling in the base class:
https://github.com/nautechsystems/nautilus_trader/blob/develop/nautilus_trader/trading/strategy.pyx#L1533