pylhe: A Lightweight Python interface to Les Houches Event files

Abstract

Les Houches Event files are a standard format for Monte Carlo event generators in high-energy physics. pylhe is a lightweight pure-Python library for reading and writing LHE event data. It supports .lhe and compressed .lhe.gz files, implements the widely used LHE 3.0 features including multiple event weights and generator metadata, and also supports the recent HDF5-based LHEH5 format. By exposing events through a pythonic iterator and shared data structures, pylhe enables memory-efficient processing of large event samples without loading entire files into memory. The library also supports format conversion and integration with modern analysis workflows, including columnar analysis with Awkward Array and downstream machine-learning applications.