How can I calculate the Residual Standard Error in Python using statsmodels?

You can easily calculate the RSE using the `statsmodels` library in Python. After fitting a regression model (e.g., OLS), the model summary object usually contains the RSE. If you're working with the results object `results`, you can often access it directly or calculate it manually. A common way is `results.mse_resid**0.5` which represents the square root of the mean squared error of the residuals.