pythonradex: a fast Python re-implementation of RADEX with extended functionality

A common task in astronomical research is to estimate the physical parameters (temperature, mass, density etc.) of a gas by using observed line emission. This often requires a calculation of how the radiation propagates via emission and absorption (so-called radiative transfer). In radio and infrared astronomy, the Fortran code RADEX (van der Tak et al., 2007) is a popular tool to solve the non-LTE radiative transfer of a uniform medium in a simplified geometry. I present pythonradex, a Python re-implementation of RADEX. Written in Python, it provides an easy and intuitive user interface, improved performance as well as additional functionality not included in RADEX, such as continuum effects and overlapping lines. In addition, pythonradex provides a self-consistent computation of the total flux for all geometries, including spherical geometries.