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Newbie looking for help

  • I've made myself a indicator and a strategy, and I can see it buying and selling. I want to dig more into it to see how I can improve it by printing out the value of my indicator from inside my strategy, but anytime I try to print anything inside my strategy or indicator I get
    <backtrader.linebuffer.LineBuffer object at 0x7feab75cf5f8> or something similar.
    How do I properly print out the values so I can see then improve my strategy & indicator?

    import backtrader as bt
    from indicators import efjay_indicator as ei
     class DevMomentum(bt.SignalStrategy):
    def __init__(self):
        ey = ei.EyIndicator(
        self.buy_sig = (ey > 0.45)
        self.sell_sig = (ey < 0.45)
    def next(self):
        if not self.position:
            if self.buy_sig:
            if self.sell_sig:


  • Hi @wysest

    You can do it like this:


    This will give you the most recent value. Use [-1] for the second most recent and so on. (This is a little different to python lists where [-1] will give you the last item. I think there is a note on this in the docs

  • Quickstart - Our first strategy:

    class TestStrategy(bt.Strategy):
        def log(self, txt, dt=None):
            ''' Logging function for this strategy'''
            dt = dt or self.datas[0]
            print('%s, %s' % (dt.isoformat(), txt))
        def __init__(self):
            # Keep a reference to the "close" line in the data[0] dataseries
            self.dataclose = self.datas[0].close
        def next(self):
            # Simply log the closing price of the series from the reference
            self.log('Close, %.2f' % self.dataclose[0])

  • import backtrader as bt
    import math
    class eIndicator(bt.Indicator):
        lines = ('e',)
        params = (('period', 15),)
        def __init__(self):
            self.e_price_avg = bt.indicators.ExponentialMovingAverage(
            self.e_price_avg_2 = bt.indicators.ExponentialMovingAverage(
                period=self.params.period * 2
            self.price_rev = (self.e_price_avg_2 - self.e_price_avg) / self.e_price_avg
            self.lines.e = self.price_rev
        def next(self):

    Okay that works inside my strategy to see the line value! Perfect.
    How about inside my indicator (shown above), how can I print the e_price_avg and e_price_avg2 for further info. Thanks! I'm just trying to calculate the percent different between two EMAs. Is this even the proper way to do it? I made it by looking at the Indicator development page but I may have misunderstood some things.

  • administrators

    @wysest said in Newbie looking for help:

    How about inside my indicator (shown above), how can I print the e_price_avg and e_price_avg2 for further info.

    It would seem obvious following what @ThatBlokeDave and @ab_trader have shown you, which is to print index [0]

    Have you tried it?

  • @backtrader Ahh. I did try that but I did it inside of the init function, but tried inside the next function this time and it worked. Thanks :)

  • administrators

    You then need to read this: Docs - Platform Concepts and see Stage1 and Stage2

  • @backtrader Just what I needed, didn't realize this existed. Thanks again! Will be sure to scour the documentation more before any other questions I may have.

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