bt - Flexible Backtesting for Python¶
What is bt?¶
bt is a flexible backtesting framework for Python used to test quantitative
trading strategies. Backtesting is the process of testing a strategy over a given
data set. This framework allows you to easily create strategies that mix and match
Algos. It aims to foster the creation of easily testable, re-usable and
flexible blocks of strategy logic to facilitate the rapid development of complex
The goal: to save quants from re-inventing the wheel and let them focus on the important part of the job - strategy development.
bt is coded in Python and joins a vibrant and rich ecosystem for data analysis. Numerous libraries exist for machine learning, signal processing and statistics and can be leveraged to avoid re-inventing the wheel - something that happens all too often when using other languages that don’t have the same wealth of high-quality, open-source projects.
bt is built atop ffn - a financial function library for Python. Check it out!
A Quick Example¶
Here is a quick taste of bt:
A Simple Strategy Backtest¶
Let’s create a simple strategy. We will create a monthly rebalanced, long-only strategy where we place equal weights on each asset in our universe of assets.
First, we will download some data. By default,
bt.get (alias for ffn.get) downloads the Adjusted Close from Yahoo! Finance. We will download some data starting on January 1, 2010 for the purposes of this demo.
# fetch some data data = bt.get('spy,agg', start='2010-01-01') print data.head()
spy agg Date 2010-01-04 98.214371 84.963075 2010-01-05 98.474354 85.349609 2010-01-06 98.543685 85.300266 2010-01-07 98.959667 85.201575 2010-01-08 99.288981 85.250923
# create the strategy s = bt.Strategy('s1', [bt.algos.RunMonthly(), bt.algos.SelectAll(), bt.algos.WeighEqually(), bt.algos.Rebalance()])
Finally, we will create a
Backtest, which is the logical combination of a strategy with a data set.
Once this is done, we can run the backtest and analyze the results.
# create a backtest and run it test = bt.Backtest(s, data) res = bt.run(test)
s1 0% 100% [############################# ] | ETA: 00:00:00
# first let's see an equity curve res.plot()
# ok and what about some stats? res.display()
Stat s1 ------------------- ---------- Start 2010-01-03 End 2017-02-22 Risk-free rate 0.00% Total Return 81.30% Daily Sharpe 1.19 Daily Sortino 1.57 CAGR 8.69% Max Drawdown -7.83% Calmar Ratio 1.11 MTD 2.08% 3m 4.08% 6m 3.26% YTD 3.11% 1Y 12.04% 3Y (ann.) 6.82% 5Y (ann.) 8.12% 10Y (ann.) 8.69% Since Incep. (ann.) 8.69% Daily Sharpe 1.19 Daily Sortino 1.57 Daily Mean (ann.) 8.61% Daily Vol (ann.) 7.23% Daily Skew -0.35 Daily Kurt 3.80 Best Day 2.48% Worst Day -3.11% Monthly Sharpe 1.41 Monthly Sortino 2.61 Monthly Mean (ann.) 8.61% Monthly Vol (ann.) 6.10% Monthly Skew 0.01 Monthly Kurt 0.18 Best Month 5.69% Worst Month -3.39% Yearly Sharpe 1.62 Yearly Sortino - Yearly Mean 7.25% Yearly Vol 4.46% Yearly Skew 0.15 Yearly Kurt -0.71 Best Year 14.10% Worst Year 1.17% Avg. Drawdown -0.79% Avg. Drawdown Days 13.31 Avg. Up Month 1.64% Avg. Down Month -1.27% Win Year % 100.00% Win 12m % 96.00%
# ok and how does the return distribution look like? res.plot_histogram()
# and just to make sure everything went along as planned, let's plot the security weights over time res.plot_security_weights()
Modifying a Strategy¶
Now what if we ran this strategy weekly and also used some risk parity style approach by using weights that are proportional to the inverse of each asset’s volatility? Well, all we have to do is plug in some different algos. See below:
# create our new strategy s2 = bt.Strategy('s2', [bt.algos.RunWeekly(), bt.algos.SelectAll(), bt.algos.WeighInvVol(), bt.algos.Rebalance()]) # now let's test it with the same data set. We will also compare it with our first backtest. test2 = bt.Backtest(s2, data) # we include test here to see the results side-by-side res2 = bt.run(test, test2) res2.plot()
s2 0% 100% [############################# ] | ETA: 00:00:00
Stat s1 s2 ------------------- ---------- ---------- Start 2010-01-03 2010-01-03 End 2017-02-22 2017-02-22 Risk-free rate 0.00% 0.00% Total Return 81.30% 40.79% Daily Sharpe 1.19 1.45 Daily Sortino 1.57 2.00 CAGR 8.69% 4.91% Max Drawdown -7.83% -4.07% Calmar Ratio 1.11 1.21 MTD 2.08% 1.56% 3m 4.08% 2.66% 6m 3.26% 0.47% YTD 3.11% 2.27% 1Y 12.04% 5.49% 3Y (ann.) 6.82% 3.97% 5Y (ann.) 8.12% 4.02% 10Y (ann.) 8.69% 4.91% Since Incep. (ann.) 8.69% 4.91% Daily Sharpe 1.19 1.45 Daily Sortino 1.57 2.00 Daily Mean (ann.) 8.61% 4.85% Daily Vol (ann.) 7.23% 3.34% Daily Skew -0.35 -0.29 Daily Kurt 3.80 2.87 Best Day 2.48% 1.20% Worst Day -3.11% -1.13% Monthly Sharpe 1.41 1.68 Monthly Sortino 2.61 2.61 Monthly Mean (ann.) 8.61% 5.04% Monthly Vol (ann.) 6.10% 3.00% Monthly Skew 0.01 -0.59 Monthly Kurt 0.18 0.03 Best Month 5.69% 1.91% Worst Month -3.39% -2.09% Yearly Sharpe 1.62 1.61 Yearly Sortino - - Yearly Mean 7.25% 4.08% Yearly Vol 4.46% 2.53% Yearly Skew 0.15 -0.45 Yearly Kurt -0.71 -0.03 Best Year 14.10% 7.02% Worst Year 1.17% -0.13% Avg. Drawdown -0.79% -0.40% Avg. Drawdown Days 13.31 13.28 Avg. Up Month 1.64% 0.83% Avg. Down Month -1.27% -0.69% Win Year % 100.00% 85.71% Win 12m % 96.00% 94.67%
As you can see, the strategy logic is easy to understand and more importantly, easy to modify. The idea of using simple, composable Algos to create strategies is one of the core building blocks of bt.
- Transaction Cost Modeling
Through the use of a commission function and instrument-specific, time-varying bid/offer spreads passed to the
- Fixed Income
Strategies can include coupon-paying instruments such as bonds, unfunded instruments such as swaps, holding costs, and the option for notional weighting. These are extensions of the tree structure.
- Charting and Reporting
bt also provides many useful charting functions that help visualize backtest results. We also plan to add more charts, tables and report formats in the future, such as automatically generated PDF reports.
- Detailed Statistics
Furthermore, bt calculates a bunch of stats relating to a backtest and offers a quick way to compare these various statistics across many different backtests via
Future development efforts will focus on:
Due to the flexible nature of bt, a trade-off had to be made between usability and performance. Usability will always be the priority, but we do wish to enhance the performance as much as possible.
We will also be developing more algorithms as time goes on. We also encourage anyone to contribute their own algos as well.
- Charting and Reporting
This is another area we wish to constantly improve on as reporting is an important aspect of the job. Charting and reporting also facilitate finding bugs in strategy logic.
- Installation Guide
- All About Algos
- The Tree Structure