'Calculate the sharpe ratio of our equity_returns.
Expects benchmark_return to be, for example, 0.01 for 1%'

def calculate_sharpe(self, benchmark_return=0.0):

    excess_returns = (pd.Series(self.equity_returns) - (benchmark_return / 252))
    return round(self.annualised_sharpe(excess_returns), 4)
