doc/master/rfile003__ttree_8py.html

import array

import os


import ROOT


def read_ttree_from_rfile(fileName):

    # Open an existing ROOT file for reading (will throw an exception if `fileName` cannot be read).

    # IMPORTANT! This file must remain open while reading data from the tree.

    with ROOT.RFile.Open(fileName) as file:

        # Get back the TTree from the file

        tree = file.Get("tree")

        floatVal = array.array("f", [0])

        tree.SetBranchAddress("floatBranch", floatVal)


        for i in range(tree.GetEntries()):

            tree.GetEntry(i)

            print(f"value[{i}] = {floatVal[0]}")


fileName = "rfile_ttree_py.root"

try:

    # Note that TTree cannot be written to RFile, so we use RDataFrame to write it instead.

    ROOT.RDataFrame(10).Define("floatBranch", "static_cast<float>(rdfentry_)").Snapshot("tree", fileName)


    read_ttree_from_rfile(fileName)

    os.remove(fileName)

except FileNotFoundError:

    pass

ROOT::RDataFrame
ROOT's RDataFrame offers a modern, high-level interface for analysis of data stored in TTree ,...
Definition RDataFrame.hxx:50

ROOT::RFile::Open
static std::unique_ptr< RFile > Open(std::string_view path, const ROpenOptions &opts=ROpenOptions())
Opens the file for reading.
Definition RFile.cxx:205