Porting the LSST Data Management Pipeline Software to Python 3
This work addresses a critical software maintenance problem for the LSST astronomy community, but it is incremental as it focuses on porting existing code rather than developing new methods.
The LSST data management pipeline, with over 100,000 lines of Python 2 code, needed migration to Python 3 before support ended in 2020, and the team used the Python future package to enable simultaneous support for Python 2 and 3 during the transition, reporting on the current status and challenges encountered.
The LSST data management science pipelines software consists of more than 100,000 lines of Python 2 code. LSST operations will begin after support for Python 2 has been dropped by the Python community in 2020, and we must therefore plan to migrate the codebase to Python 3. During the transition period we must also support our community of active Python 2 users and this complicates the porting significantly. We have decided to use the Python future package as the basis for our port to enable support for Python 2 and Python 3 simultaneously, whilst developing with a mindset more suited to Python 3. In this paper we report on the current status of the port and the difficulties that have been encountered.