Having trouble understanding how to get VWR analyzer to work

[Russell Turner]

I am new to this and the examples for the VWR analyzer in the help documentation are too complicated for me to understand. I have been able to run this code:

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

from datetime import datetime

import backtrader as bt
import backtrader.analyzers as btanalyzers

# Create a Strategy
class TestStrategy(bt.Strategy):

    def log(self, txt, dt=None):
        ''' Logging function for this strategy'''
        dt = dt or self.datas[0].datetime.date(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])

if __name__ == '__main__':
    # Create a cerebro enity
    cerebro = bt.Cerebro()

    data = bt.feeds.YahooFinanceData(dataname='SPY', fromdate=datetime(2019, 1, 1), todate=datetime(2019, 12, 31))
    cerebro.adddata(data)

    # Add a strategy
    cerebro.addstrategy(TestStrategy)

    # Analyzer
    cerebro.addanalyzer(btanalyzers.VWR, _name='myvwr')

    thestrats = cerebro.run()
    thestrat = thestrats[0]

    print('VWR: ', thestrat.analyzers.myvwr.get_analysis())

    # Plot the result
    cerebro.plot()

I can change 'SPY' to any other ticker symbol... For example Apple... or Microsoft... or whatever. I can change the date range easy enough too. But I can't figure out how to get a value for VWR other than "0." At first I didnt realize I needed a strategy in order to get VWR but then someone told me I needed a strategy to get VWR. So I made a strategy as you can see above... but it still shows 0 for VWR.

[run-out]

You have no trades, your VWR will be 0.