An indicator that knows if I have a position or not

[Kristofer Monisit]

I am building an indicator that does one thing if I'm not in the trade, and does another if I'm in.

Is it possible for a subclass of Indicators to access the position attribute of the Strategy?

Of course, this indicator cannot be pre-computed, but is emits data as the backtest progresses.

The following code surely raises AttributeError: 'Lines_LineSeries_LineIterator_DataAccessor_Indicat' object has no attribute 'position'

class CustomIndicator(bt.Indicator):
    lines = ('custom_indicator',)
    params = (('period', 14), )
    
    def next(self):
        if self.position:
            self.lines.custom_indicator[0] = True and is_something_else_true()
            self.do_something()
        else:
            self.lines.custom_indicator[0] = False
            self.do_nothing()

[momentum]

The strategy can turn on/off a parameter of the indicator according to whether in trade or not. Have a look at the dynamic indicator example
https://www.backtrader.com/blog/posts/2018-02-06-dynamic-indicator/dynamic-indicator.html

[Kristofer Monisit]

@momentum Thanks! I would add that Cerebro will have to be instantiated with Cerebro(runonce=False). Otherwise, if I use the default, i.e. runonce=True, all indicators would be precalculated all the way to the end, and they would not be able to observe if a trade is open or not.

Reference for the runonce argument:
https://www.backtrader.com/docu/cerebro.html?highlight=vectorize#backtrader.Cerebro

[momentum]

I even like better the _nextforce = True pointed out to me by @backtrader some time ago.

class CustomIndicator(bt.Indicator):
    _nextforce = True
...