  We present PEANUTS (Propagation and Evolution of Active NeUTrinoS), an
open-source Python package for the automatic computation of solar neutrino
spectra and active neutrino propagation through Earth. PEANUTS is designed to
be fast, by employing analytic formulae for the neutrino propagation through
varying matter density, and flexible, by allowing the user to input arbitrary
solar models, custom Earth density profiles and general detector locations. It
provides functionalities for a fully automated simulation of solar neutrino
fluxes at a detector, as well as access to individual routines to perform more
specialised computations. The software has been extensively tested against the
results of the SNO experiment, providing excellent agreement with their
results. In addition, the present text contains a pedagogical derivation of the
relations needed to compute the oscillated solar neutrino spectra, neutrino
propagation through Earth and nadir exposure of an experiment.
