pyCubexR (https://github.com/extra-p/pycubexr) is a Python package for reading the Cube4 (.cubex) file format. Cube is used as a performance report explorer for Scalasca and Score-P. It is used as a generic tool for displaying a multidimensional performance space consisting of the dimensions (i) performance metric, (ii) call path, and (iii) system resource. Each dimension can be represented as a tree, where non-leaf nodes of the tree can be collapsed or expanded to achieve the desired level of granularity. The Cube4 (.cubex) data format is provided for Cube files produced with the Score-P performance instrumentation and measurement infrastructure or the Scalasca version 2.x trace analyzer (and other compatible tools). This specific version of the code is intended to be used for the evaluation of cost effective measurement sampling strategies for empirical performance modeling using reinforcement learning, and Gaussian progress regression (GPR).