ESP is a way to estimate galaxy spectra using Principal Component Analysis (PCA) and Gaussian Processes. Starting from a set of known spectra and a set of bandpasses you can predict spectra for other points in the color space of your bands both interpolating and extrapolating throughout the color space.
For more information read the paper.
ESP is pip installable. From the command line run:
pip install esphot
Now to use from python, just:
import esp
See the example jupyter notebook in the examples folder.