Gammapy is a python package for the analysis of gamma-ray astronomical data. This open-source software has been selected as the official analysis tool of the Cherenkov Telescope Array (CTA), and it is already used to analyse data from the current generation of gamma-ray instruments. Open-source analysis tools are revolutionising a discipline whose results have been traditionally obtained with proprietary data and software, granting full reproducibility of results and allowing for combination of data from different instruments. The paper presentd the first major release of the software.