import arch

# a standard GARCH(1,1) model
garch = arch_model(returns, vol='garch', p=1, o=0, q=1)
garch_fitted = garch.fit()

# one-step out-of sample forecast
garch_forecast = garch_fitted.forecast(horizon=1)
predicted_et = garch_forecast.mean['h.1'].iloc[-1]