Plotting more than one line in an indicator

[Eddy Bennett]

How do you plot more than one line on a chart with an indicator?

The documentation mentions the LinePlotterIndicator but it doesn't explain how to call it.

For testing I'm just creating a simple Indicator with two moving averages which I would like to plot on the chart:

# Import the backtrader platform
import backtrader as bt
import math

class ProjectedMovingAverageIndicator(bt.Indicator):
  lines = ('smaSlow','smaFast',)
  params = (('periodSlow', 200),('periodFast', 100),)
  plotinfo = dict(subplot=False)

  def __init__(self):
      self.addminperiod(self.params.periodSlow)
      
  def next(self):
      datasum = math.fsum(self.data.close.get(size=self.p.periodSlow))
      self.lines.smaSlow[0] = datasum / self.p.periodSlow
      self.lines.smaFast[0] = datasum / self.p.periodFast
      print(self.lines.smaSlow[0],' ', self.lines.smaFast[0])

  def signal(self):
    if self.lines.smaFast[-1] < self.lines.smaSlow[-1] and self.lines.smaFast[0] > self.lines.smaSlow[0]:
        signal = True
    else:
        signal = False
    #print(signal)
    return signal

Thanks

[ab_trader]

bt should plot all indicator lines by default when you initiate your indicator in the strategy. For example, add bollinger bands indicator in your strategy and it will be plotted. So no need to use LinePlotterIndicator.

[Eddy Bennett]

Thanks for the speedy reply @ab_trader. That's what I thought should happen, but as you can see in the attached it's not happening. I must be doing something wrong, I looked at the Bollinger band indicator code on Github and can see that the lines are being declared in the init function as opposed to next:

def __init__(self):
        self.lines.mid = ma = self.p.movav(self.data, period=self.p.period)
        stddev = self.p.devfactor * StdDev(self.data, ma, period=self.p.period,
                                           movav=self.p.movav)
        self.lines.top = ma + stddev
        self.lines.bot = ma - stddev

        super(BollingerBands, self).__init__()

Should I be doing that instead?

Thanks


[Eddy Bennett]

Hmm image link didn't work, here is another [https://prnt.sc/vd8mek]

[Eddy Bennett]

Ok I played around a bit and got it working:

from __future__ import (absolute_import, division, print_function,
                        unicode_literals)

# Import the backtrader platform
import backtrader as bt
import math

class ProjectedMovingAverageIndicator(bt.Indicator):

  lines = ('smaSlow','smaFast',)
  params = (('periodSlow', 200),('periodFast', 100),('movav', bt.indicators.MovAv.Simple),)
  plotinfo = dict(subplot=False)
  plotlines = dict(
    smaSlow=dict(_samecolor=True),
    smaFast=dict(_samecolor=False),
    )

  def __init__(self):
    self.addminperiod(self.params.periodSlow)
    movavSlow = self.p.movav(self.data, period=self.p.periodSlow)
    movavFast = self.p.movav(self.data, period=self.p.periodFast)
    self.l.smaSlow = movavSlow #bt.Cmp(movav, self.data)
    self.l.smaFast = movavFast #bt.Cmp(movav, self.data)

  def signal(self):
    if self.lines.smaFast[-1] < self.lines.smaSlow[-1] and self.lines.smaFast[0] > self.lines.smaSlow[0]:
        signal = True
    else:
        signal = False
    #print(signal)
    return signal

Thanks