popclass: A Python Package for Classifying Microlensing Events

popclass is a Python package that provides a flexible, probabilistic framework for classifying the lens of a gravitational microlensing event.Gravitational microlensing occurs when a massive foreground object (e.g., a star, white dwarf or black hole) passes in front of and lenses the light from a distant background source.This causes an apparent brightening, and shift in position, of the background source.In most cases, characteristics of the microlensing signal do not contain enough information to definitively identify the lens type.Different lens types lie in different but overlapping regions of the characteristics of the microlensing signal.For example, black holes tend to be more massive than stars and therefore cause microlensing signals that are longer.Current Galactic simulations enable us to predict where different lens types lie in the observational space and can therefore be used to classify events (e.g., Lam et al., 2020).