doc/master/rfile002__rntuple_8py.html

import ROOT


import os


def write_rntuple_to_rfile(fileName):

    # Create a new ROOT file for writing

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

        # Define the RNTuple schema

        model = ROOT.RNTupleModel.Create()

        model.MakeField["int"]("intField")

        # Create an RNTupleWriter to append to the RFile

        with ROOT.RNTupleWriter.Append(model, "ntuple", file) as writer:

            entry = writer.CreateEntry()


            # Fill the RNTuple with data

            for i in range(10):

                entry["intField"] = i

                writer.Fill(entry)


            # `writer` will write the data to file upon exiting the with statement....

        # ...then `file` will write itself to disk in turn when exiting the outer with statement.


def read_rntuple_from_rfile(fileName):

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

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

        # Get back the RNTuple anchor from the file

        rntuple = file.Get("ntuple")


        # Create an RNTupleReader from the anchor

        with ROOT.RNTupleReader.Open(rntuple) as reader:

            entry = reader.CreateEntry()

            for i in reader.GetEntryRange():

                reader.LoadEntry(i, entry)

                print(f"value[{i}] = {entry['intField']}")


fileName = "rfile_rntuple_py.root"

try:

    write_rntuple_to_rfile(fileName)

    read_rntuple_from_rfile(fileName)

    os.remove(fileName)

except FileNotFoundError:

    pass

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

ROOT::RFile::Recreate
static std::unique_ptr< RFile > Recreate(std::string_view path, const RRecreateOptions &opts=RRecreateOptions())
Opens the file for reading/writing, overwriting it if it already exists.
Definition RFile.cxx:227

ROOT::RNTupleModel::Create
static std::unique_ptr< RNTupleModel > Create()
Definition RNTupleModel.cxx:339

ROOT::RNTupleReader::Open
static std::unique_ptr< RNTupleReader > Open(std::string_view ntupleName, std::string_view storage, const ROOT::RNTupleReadOptions &options=ROOT::RNTupleReadOptions())
Open an RNTuple for reading.
Definition RNTupleReader.cxx:189

ROOT::RNTupleWriter::Append
static std::unique_ptr< RNTupleWriter > Append(std::unique_ptr< ROOT::RNTupleModel > model, std::string_view ntupleName, TDirectory &fileOrDirectory, const ROOT::RNTupleWriteOptions &options=ROOT::RNTupleWriteOptions())
Creates an RNTupleWriter that writes into an existing TFile or TDirectory, without overwriting its co...
Definition RNTupleWriter.cxx:105