This preprint (to be submitted to the Journal of Open Source Software) describes the need and use cases for PySWMM, the Python wrapper to the EPA Stormwater Management Model (SWMM). SWMM is a dynamic rainfall-runoff model that has been used for decades to conduct single event or long-term hydrologic, hydraulic, and water quality simulations. PySWMM interfaces with the Open Water Analytics SWMM5 API and allows Pythonic access to the SWMM data model, which enables users to interact with a model during simulation time and facilitates rapid prototyping, optimization, and results post-processing.