The Electromagnetic/Circuit cosimulation method represents an effective strategy to address those problems where a radiative structure has to interact with external supporting circuitries.This method proved to be particularly valuable for MRI RF coil design where the supporting circuitry optimisation is generally of particular concern. CoSimPy, an open-source library conceived for Electromagnetic/Circuit cosimulations, is presented. CoSimPy is written in Python following an Object-oriented programming. This improves its scalability and easily allows interested scientists to collaborate, integrating and improving the library with other methods. CoSimPy is available under https://github.com/umbertozanovello/CoSimPy together with a detailed documentation providing guidelines and examples.