1. Added Benefits Easier to debug –Can dump configurations or add inline printouts –Can validate files by compiling Can use command-line arguments, environmental variables, and higher-level Python functions Many free tools available –See A. Hinzmann’s talk, “Visualization of the CMS Python Configuration System”

2. Design Mimic look and feel of old configuration. Result is a python data structure –Not an interactive system Use boost::python to translate into a C++ data structure Translated configurations in the release –Made scripts to automatically parse, translate, commit, and tag configuration include fragment files

3. New Python Config import FWCore.ParameterSet.Config as cms process = cms.Process(“foo”) process.jet50Filter = cms.EDFilter(“JetFilter”, minPt = cms.double(50.) ) process.jet100Filter = process.jet50Filter.clone() process.jet100Filter.minPt = 100. process.load(“Jets.Reco.JetReco_cfi”) process.jetReco.coneSize = 0.7 process.jet50to100Filter = cms.Sequence(process.jetFilter50+~process.jetFilter100) process.jet50to100 = cms.Path(process.jetReco*process.jet50to100Filter)

4. Old Custom Language process = foo { module jet50Filter = JetFilter { float minPt = 50. } module jet100Filter = jet50Filter.clone() jet100Filter.minPt = 100. include “Jets/Reco/data/JetReco.cfi” replace jetReco.coneSize = 0.7 sequence jet50to100Filter = {jetFilter50&!jetFilter100} path jet50to100 = {jetReco, jet50to100Filter} }

5. Why Switch to Python? Previously, CMS used a custom configuration language – Parsed using flex/bison Users needed to be able to copy, share, and modify fragments – Users customizing their job – Production system splitting jobs, setting random seeds, etc. Required a lot of effort to support these operations for all data types

6. CMS Job Configuration Complex hierarchical structure –24 data types –10 module types –11 types of execution control statements & operators Release contains ~6000 configuration files –4500 shared fragments –1400 executable job configurations Standard full-chain simulation job defines: –700 modules –150 sequences of modules – over 13,000 configurable parameters