RadioPy is an open source Python package for radio astrophysics capable of fitting spectra of synchrotron radio emission. Adapted for supernovae in its first version, one of its main features is that it can perform a complete an automatic analysis for a sequence of supernova spectra and calculate the shockwave radius (R), the intensity of the magnetic field (B) and the circumstellar density (A) and their evolution over time. Its other main feature is its object-oriented architecture that sets a standard on how to record the data regarding the non-thermal emission of radio sources and at the same time provides an easily extendible structure designed to evolve. The design of the architecture makes it easy to use and to extend, allowing researchers all over the world to download RadioPy and implement their own models and methods easily. The first version of this package contains 15 classes and 126 methods (version: June 2017) and provides robust algorithms for fitting spectra to an approximation of the Synchrotron Self-Absorption (SSA) model. The development of those algorithms and the goodness of the approximation are reasonable and they are discussed in the present document. A comparison between the results in the literature and those obtained with RadioPy for a case study of the radio evolution of supernova SN2011dh proved the capabilities of the software tool