A package that provides an interface for downloading and processing the Marktstammdatenregister (MaStR). The Marktstammdatenregister (MaStR) is a German register provided by the German Federal Network Agency (Bundesnetzagentur / BNetza) that keeps track of all power and gas units located in Germany. It is a daily growing dataset with more than 8.2 million data points covering electricity and gas production units, electricity and gas consumers, storages, grids, and energy market participants (as of spring 2024). Generally, the MaStR data can be accessed via various options: browse, filter and download online download daily provided dumps access via the web service The python package open-mastr provides an interface for accessing the data and contributes to improving the usability of the access options above. This repository is intended for people who wish to simply work with the MaStR data and do not want to deal with the individual obstacles to data access of the three options above. It facilitates access to the daily provided MaStR dumps with download methods (bulk) and by parsing the XML files to a relational database. Furthermore, the software provides a Python wrapper to access the MaStR SOAP web service (API).