doc/v628/pyroot006__tcontext__context__manager_8py.html

import os


import ROOT

from ROOT import TDirectory, TFile


# Sometimes it is useful to have multiple open files at once. In such cases,

# the current directory will always be the file that was open last.

file_1 = TFile("pyroot006_file_1.root", "recreate")

file_2 = TFile("pyroot006_file_2.root", "recreate")

print("Current directory: '{}'.\n".format(ROOT.gDirectory.GetName()))

# Changing directory into another file can be safely done through a TContext

# context manager.

with TDirectory.TContext(file_1):

    # Inside the statement, the current directory is file_1

    print("Current directory: '{}'.\n".format(ROOT.gDirectory.GetName()))

    histo_1 = ROOT.TH1F("histo_1", "histo_1", 10, 0, 10)

    file_1.WriteObject(histo_1, "my_histogram")


# After the context, the current directory is restored back to file_2. Also, the

# two files are kept open. This means that objects read, written or modified

# inside the context are still available afterwards.

print("Current directory: '{}'.\n".format(ROOT.gDirectory.GetName()))

if file_1.IsOpen() and file_2.IsOpen():

    print("'{}' and '{}' are open.\n".format(file_1.GetName(), file_2.GetName()))


# TContext and TFile context managers can also be used in conjunction, allowing

# for safely:

# - Opening a file, creating, modifying, writing and reading objects in it.

# - Closing the file, storing it on disk.

# - Restoring the previous value of gDirectory to the latest file opened before

#   this context, rather than to the global ROOT.gROOT

# Remember that the TContext must be initialized before the TFile, otherwise the

# current directory would already be set to the file opened for this context.

with TDirectory.TContext(), TFile("pyroot006_file_3.root", "recreate") as f:

    print("Current directory: '{}'.\n".format(ROOT.gDirectory.GetName()))

    histo_2 = ROOT.TH1F("histo_2", "histo_2", 10, 0, 10)

    f.WriteObject(histo_2, "another_histogram")


print("Current directory: '{}'.\n".format(ROOT.gDirectory.GetName()))


# Cleanup the files created for this tutorial

file_1.Close();

file_2.Close();

for i in range(1, 4):

    os.remove("pyroot006_file_{}.root".format(i))

format
Option_t Option_t TPoint TPoint const char GetTextMagnitude GetFillStyle GetLineColor GetLineWidth GetMarkerStyle GetTextAlign GetTextColor GetTextSize void char Point_t Rectangle_t WindowAttributes_t Float_t Float_t Float_t Int_t Int_t UInt_t UInt_t Rectangle_t Int_t Int_t Window_t TString Int_t GCValues_t GetPrimarySelectionOwner GetDisplay GetScreen GetColormap GetNativeEvent const char const char dpyName wid window const char font_name cursor keysym reg const char only_if_exist regb h Point_t winding char text const char depth char const char Int_t count const char ColorStruct_t color const char Pixmap_t Pixmap_t PictureAttributes_t attr const char char ret_data h unsigned char height h Atom_t Int_t ULong_t ULong_t unsigned char prop_list Atom_t Atom_t Atom_t Time_t format
Definition TGWin32VirtualXProxy.cxx:249

TDirectory::TContext
TDirectory::TContext keeps track and restore the current directory.
Definition TDirectory.h:89

TFile
A ROOT file is a suite of consecutive data records (TKey instances) with a well defined format.
Definition TFile.h:51