SMABacktester.py

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
from itertools import product
plt.style.use("seaborn-v0_8")


class SMABacktester():
    ''' Class for the vectorized backtesting of SMA-based trading strategies.
    '''
    
    def __init__(self, symbol, SMA_S, SMA_L, start, end):
        '''
        Parameters
        ----------
        symbol: str
            ticker symbol (instrument) to be backtested
        SMA_S: int
            moving window in bars (e.g. days) for shorter SMA
        SMA_L: int
            moving window in bars (e.g. days) for longer SMA
        start: str
            start date for data import
        end: str
            end date for data import
        '''
        self.symbol = symbol
        self.SMA_S = SMA_S
        self.SMA_L = SMA_L
        self.start = start
        self.end = end
        self.results = None 
        self.get_data()
        self.prepare_data()
        
    def __repr__(self):
        return "SMABacktester(symbol = {}, SMA_S = {}, SMA_L = {}, start = {}, end = {})".format(self.symbol, self.SMA_S, self.SMA_L, self.start, self.end)
        
    def get_data(self):
        ''' Imports the data from forex_pairs.csv (source can be changed).
        '''
        raw = pd.read_csv("forex_pairs.csv", parse_dates = ["Date"], index_col = "Date")
        raw = raw[self.symbol].to_frame().dropna()
        raw = raw.loc[self.start:self.end].copy()
        raw.rename(columns={self.symbol: "price"}, inplace=True)
        raw["returns"] = np.log(raw / raw.shift(1))
        self.data = raw
        
    def prepare_data(self):
        '''Prepares the data for strategy backtesting (strategy-specific).
        '''
        data = self.data.copy()
        data["SMA_S"] = data["price"].rolling(self.SMA_S).mean()
        data["SMA_L"] = data["price"].rolling(self.SMA_L).mean()
        self.data = data
        
    def set_parameters(self, SMA_S = None, SMA_L = None):
        ''' Updates SMA parameters and the prepared dataset.
        '''
        if SMA_S is not None:
            self.SMA_S = SMA_S
            self.data["SMA_S"] = self.data["price"].rolling(self.SMA_S).mean()
        if SMA_L is not None:
            self.SMA_L = SMA_L
            self.data["SMA_L"] = self.data["price"].rolling(self.SMA_L).mean()
            
    def test_strategy(self):
        ''' Backtests the SMA-based trading strategy.
        '''
        data = self.data.copy().dropna()
        data["position"] = np.where(data["SMA_S"] > data["SMA_L"], 1, -1)
        data["strategy"] = data["position"].shift(1) * data["returns"]
        data.dropna(inplace=True)
        data["creturns"] = data["returns"].cumsum().apply(np.exp)
        data["cstrategy"] = data["strategy"].cumsum().apply(np.exp)
        self.results = data
       
        perf = data["cstrategy"].iloc[-1] # absolute performance of the strategy
        outperf = perf - data["creturns"].iloc[-1] # out-/underperformance of strategy
        return round(perf, 6), round(outperf, 6)
    
    def plot_results(self):
        ''' Plots the performance of the trading strategy and compares to "buy and hold".
        '''
        if self.results is None:
            print("Run test_strategy() first.")
        else:
            title = "{} | SMA_S = {} | SMA_L = {}".format(self.symbol, self.SMA_S, self.SMA_L)
            self.results[["creturns", "cstrategy"]].plot(title=title, figsize=(12, 8))
    
    def optimize_parameters(self, SMA_S_range, SMA_L_range):
        ''' Finds the optimal strategy (global maximum) given the SMA parameter ranges.

        Parameters
        ----------
        SMA_S_range, SMA_L_range: tuple
            tuples of the form (start, end, step size)
        '''
        
        combinations = list(product(range(*SMA_S_range), range(*SMA_L_range)))
        
        # test all combinations
        results = []
        for comb in combinations:
            self.set_parameters(comb[0], comb[1])
            results.append(self.test_strategy()[0])
        
        best_perf = np.max(results) # best performance
        opt = combinations[np.argmax(results)] # optimal parameters
        
        # run/set the optimal strategy
        self.set_parameters(opt[0], opt[1])
        self.test_strategy()
                   
        # create a df with many results
        many_results =  pd.DataFrame(data = combinations, columns = ["SMA_S", "SMA_L"])
        many_results["performance"] = results
        self.results_overview = many_results
                            
        return opt, best_perf