CASSIS-LTE-Python is a Python module based on the same LTE algorithm as the one used in CASSIS (ascl:1402.013). Based on the user's description of an observed source, the module builds a function representing the LTE model of the source, and performs the minimization of this function with respect to the observed spectrum (if pointed mode) or spectra (if mapping mode). The source description consists in a series of components arranged in an onion-like structure ; each component is characterized by a size, a velocity, an excitation temperature, a line width and the column densities of the species present in the component. CASSIS-LTE-Python uses the non-linear least-squares minimization package lmfit (ascl:1606.014), so that the user can choose from any minimization algorithm available in lmfit.
Other key features include : supporting observations made with multiple telescopes, using constraints on spectroscopic parameters for each species, fitting an entire spectrum or only selected frequency windows, taking into account a continuum in the model for continuum-free observations, possibility to use a spatial mask for data cubes.