Using ROOT with python

Overview

Teaching: 0 min
Exercises: 0 min

Questions

• Can I call ROOT from python?

Objectives

• Find resources

PyROOT

The PyROOT project started with Wim Lavrijsen in the late `00s and became very popular, paralleling the rise of more general python tools within the community. Python has become the primary analysis language for the majority of HEP experimentalists. It has a rich ecosystem that is constantly evolving. This is a good thing because it means that improvements and new tools are always being developed, but it can sometimes be a challenge to keep up with the latest and greatest projects! :)

If you want to learn how to use PyROOT, you can go through some individual examples here, or a more guided tutorial here.

Feel free to challenge yourself to rewrite the previous C++ code using PyROOT!

Using the Python docker container

The tools in the Python docker container will allow you to can easily open and analyze ROOT files. This is useful for when you make use of the CMS open data tools to skim some subset of the open data and then copy it to your local laptop, desktop, or perhaps an HPC cluster at your home institution.

If you completed the Docker pre-exercises you should already have worked through this episode, under Download the docker images for ROOT and python tools and start container, and you will have

• a working directory cms_open_data_python on your local computer
• a docker container with name my_python created with the working directory cms_open_data_python mounted into the /code directory of the container.

Start your python container with

docker start -i my_python

In the container, you will be in the /code directory and it shares the files with your local cms_open_data_python directory.

If you want to test out the installation, from within Docker you can launch and interactive python session by typing python (in Docker) and then trying

import uproot
import awkward as ak

If you don’t get any errors then congratulations! You have a working environment and you are ready to perform some HEP analysis with your new python environment!

Key Points

• PyROOT is a complete interface to the ROOT libraries