doc/master/rfile001__basics_8py.html

import ROOT


import os


def write_hist_to_rfile(fileName):

    # Create a histogram to write to the file

    hist = ROOT.TH1D("hist", "hist", 10, 0, 100)

    hist.FillRandom("gaus", 1000)


    # Create a new ROOT file for writing

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

        # Put objects into the file (in this case we write the same object multiple times

        # under different paths). Note that the ownership of `hist` is untouched by `file.Put`.

        file.Put(hist.GetName(), hist)

        file.Put(f"a/{hist.GetName()}", hist)

        file.Put(f"a/b/{hist.GetName()}", hist)


    # When the `with` statement is exited the file will write itself to disk and close itself.

    # To manually write the file without closing it, one can use `file.Flush()`.


def read_hist_from_rfile(fileName):

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

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

        # Iterate all keys of all objects in the file (this excludes directories by default - see the documentation of

        # ListKeys() for all the options).

        for key in file.ListKeys():

            # Retrieve the objects from the file. `file.Get` will return an object of the proper type or None if

            # the object isn't there.

            # Once an object is retrieved, it is fully owned by the application, so it survives even if `file` is closed.

            hist = file.Get(key.GetPath())

            if hist is not None:

                continue

            print(f"{key.GetClassName()} at {key.GetPath()};{key.GetCycle()}:")

            print(f"  entries: {hist.GetEntries()}")


fileName = "rfile_basics_py.root"

try:

    write_hist_to_rfile(fileName)

    read_hist_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