close position with some note

Discussed in https://github.com/kernc/backtesting.py/discussions/1298

^{Originally posted by silverwolf-x August 4, 2025}
I want to add reasons for the end of certain trades, for example, how do I tag the ending order of the buy trade from 2013-02-26, indicating that I ended the trade due to reason R, and write R into this order and trade.

from datetime import date
from backtesting import Backtest, Strategy
from backtesting.lib import crossover

from backtesting.test import SMA, GOOG
class SmaCross(Strategy):
    n1 = 10
    n2 = 20

    def init(self):
        close = self.data.Close
        self.sma1 = self.I(SMA, close, self.n1)
        self.sma2 = self.I(SMA, close, self.n2)

    def next(self):
        if not self.data.index[-1].date() >= date(2013, 2, 1):
            if crossover(self.sma1, self.sma2):
                self.position.close()
                self.buy()
            elif crossover(self.sma2, self.sma1):
                self.position.close()
                self.sell()
        else:
            if self.data.index[-1].date() == date(2013, 2, 26):
                self.buy(size=1, tag="2013-02-26buy")
            if self.data.index[-1].date() == date(2013, 2, 27):
                self.position.close()
bt = Backtest(GOOG, SmaCross, cash=10000, commission=0.002)

stats = bt.run()

My Hope:

when calling either self.position.close(reason="R") or self.trade.close(reason="R"), I want to update the tag of any canceled order to "R". This makes sense because, at that point, the order looks like this:

{
 'is_contingent': False,
 'is_long': False,
 'is_short': True,
 'limit': None,
 'parent_trade': <Trade size=34 time=2146- price=801.1- pl=173 tag=2013-02-26buy>,
 'size': -34.0,
 'sl': None,
 'stop': None,
 'tag': '2013-02-26buy',
 'tp': None
}

Since the order already contains a parent_trade, updating the tag to "R" clearly indicates that the reason for closing the trade was "R".

Additionally, it would be useful if trades included a new property: close_reason (e.g.), which would display "R" in such cases.

Start at the position and trade close entry points shown in the example (self.position.close() and self.trade.close()), then trace how the closing order and parent trade are represented. Define how a supplied reason should be retained in the order and trade data, including the requested close_reason; done means the example can record and expose the reason consistently.