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pyroot006_tcontext_context_manager.py
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1## \file
2## \ingroup tutorial_pyroot
3## \notebook -nodraw
4##
5## This tutorial demonstrates the usage of the TContext class as a Python context
6## manager. This functionality is related with how TFile works, so it is
7## suggested to also take a look at the pyroot005 tutorial.
8##
9## \macro_code
10## \macro_output
11##
12## \date March 2022
13## \author Vincenzo Eduardo Padulano CERN/UPV
14import os
15
16import ROOT
17from ROOT import TDirectory, TFile
18
19# Sometimes it is useful to have multiple open files at once. In such cases,
20# the current directory will always be the file that was open last.
21file_1 = TFile("pyroot006_file_1.root", "recreate")
22file_2 = TFile("pyroot006_file_2.root", "recreate")
23print("Current directory: '{}'.\n".format(ROOT.gDirectory.GetName()))
24# Changing directory into another file can be safely done through a TContext
25# context manager.
26with TDirectory.TContext(file_1):
27 # Inside the statement, the current directory is file_1
28 print("Current directory: '{}'.\n".format(ROOT.gDirectory.GetName()))
29 histo_1 = ROOT.TH1F("histo_1", "histo_1", 10, 0, 10)
30 file_1.WriteObject(histo_1, "my_histogram")
31
32# After the context, the current directory is restored back to file_2. Also, the
33# two files are kept open. This means that objects read, written or modified
34# inside the context are still available afterwards.
35print("Current directory: '{}'.\n".format(ROOT.gDirectory.GetName()))
36if file_1.IsOpen() and file_2.IsOpen():
37 print("'{}' and '{}' are open.\n".format(file_1.GetName(), file_2.GetName()))
38
39# TContext and TFile context managers can also be used in conjunction, allowing
40# for safely:
41# - Opening a file, creating, modifying, writing and reading objects in it.
42# - Closing the file, storing it on disk.
43# - Restoring the previous value of gDirectory to the latest file opened before
44# this context, rather than to the global ROOT.gROOT
45# Remember that the TContext must be initialized before the TFile, otherwise the
46# current directory would already be set to the file opened for this context.
47with TDirectory.TContext(), TFile("pyroot006_file_3.root", "recreate") as f:
48 print("Current directory: '{}'.\n".format(ROOT.gDirectory.GetName()))
49 histo_2 = ROOT.TH1F("histo_2", "histo_2", 10, 0, 10)
50 f.WriteObject(histo_2, "another_histogram")
51
52print("Current directory: '{}'.\n".format(ROOT.gDirectory.GetName()))
53
54# Cleanup the files created for this tutorial
55file_1.Close();
56file_2.Close();
57for i in range(1, 4):
58 os.remove("pyroot006_file_{}.root".format(i))
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
TDirectory::TContext keeps track and restore the current directory.
Definition: TDirectory.h:89
A ROOT file is a suite of consecutive data records (TKey instances) with a well defined format.
Definition: TFile.h:54