Pykat: Python package for modelling precision optical interferometers

\textsc{Pykat} is a Python package which extends the popular optical interferometer modelling software \textsc{Finesse}. It provides a more modern and efficient user interface for conducting complex numerical simulations, as well as enabling the use of Python's extensive scientific software ecosystem. In this paper we highlight the relationship between \textsc{Pykat} and \textsc{Finesse}, how it is used, and provide an illustrative example of how it has helped to better understand the characteristics of the current generation of gravitational wave interferometers.