Gammapy sub-package structure and data analysis workflow. The top row defines the different levels of data reduction, from lists of γ-ray-like events on the left (DL3), to high-level scientific products (DL5) on the right. The direction of the data flow is illustrated with the gray arrows. The gray folder icons represent the different sub-packages in Gammapy and names given as the corresponding Python code suffix, e.g., gammapy. data. Below each icon there is a list of the most important objects defined in the sub-package. The light gray folder icons show the sub-packages for the most fundamental data structures such as maps and IRFs. The bottom of the figure shows the high-level analysis sub-module with its dependency on the YAML file format.