Helper functions to calculate backtest returns and strategy stats.

finance_helper_funcs.py

# A few helper functions
def calcReturns(df):
  # Helper function to avoid repeating too much code
  df['returns'] = df['Close'] / df['Close'].shift(1)
  df['log_returns'] = np.log(df['returns'])
  df['strat_returns'] = df['position'].shift(1) * df['returns']
  df['strat_log_returns'] = df['position'].shift(1) * \
    df['log_returns']
  df['cum_returns'] = np.exp(df['log_returns'].cumsum()) - 1
  df['strat_cum_returns'] = np.exp(
    df['strat_log_returns'].cumsum()) - 1
  df['peak'] = df['cum_returns'].cummax()
  df['strat_peak'] = df['strat_cum_returns'].cummax()
  return df

def getStratStats(log_returns: pd.Series,
  risk_free_rate: float = 0.02):
  stats = {}  # Total Returns
  stats['tot_returns'] = np.exp(log_returns.sum()) - 1  
  
  # Mean Annual Returns
  stats['annual_returns'] = np.exp(log_returns.mean() * 252) - 1  
  
  # Annual Volatility
  stats['annual_volatility'] = log_returns.std() * np.sqrt(252)
  
  # Sortino Ratio
  annualized_downside = log_returns.loc[log_returns<0].std() * \
    np.sqrt(252)
  stats['sortino_ratio'] = (stats['annual_returns'] - \
    risk_free_rate) / annualized_downside  
  
  # Sharpe Ratio
  stats['sharpe_ratio'] = (stats['annual_returns'] - \
    risk_free_rate) / stats['annual_volatility']  
  
  # Max Drawdown
  cum_returns = log_returns.cumsum() - 1
  peak = cum_returns.cummax()
  drawdown = peak - cum_returns
  max_idx = drawdown.argmax()
  stats['max_drawdown'] = 1 - np.exp(cum_returns[max_idx]) \
    / np.exp(peak[max_idx])
  
  # Max Drawdown Duration
  strat_dd = drawdown[drawdown==0]
  strat_dd_diff = strat_dd.index[1:] - strat_dd.index[:-1]
  strat_dd_days = strat_dd_diff.map(lambda x: x.days).values
  strat_dd_days = np.hstack([strat_dd_days,
    (drawdown.index[-1] - strat_dd.index[-1]).days])
  stats['max_drawdown_duration'] = strat_dd_days.max()
  return {k: np.round(v, 4) if type(v) == np.float_ else v
          for k, v in stats.items()}