ROOT
v6-36
Reference Guide
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tcontext_context_manager.py
Go to the documentation of this file.
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## \file
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## \ingroup tutorial_io
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## \notebook -nodraw
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## This tutorial demonstrates the usage of the TContext class as a Python context
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## manager. This functionality is related with how TFile works, so it is
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## suggested to also take a look at the tfile_context_manager.py tutorial.
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##
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## \macro_code
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## \macro_output
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##
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## \date March 2022
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## \author Vincenzo Eduardo Padulano CERN/UPV
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import
os
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import
sys
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import
ROOT
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from
ROOT
import
TDirectory, TFile, gROOT
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# Sometimes it is useful to have multiple open files at once. In such cases,
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# the current directory will always be the file that was open last.
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path = str(
gROOT.GetTutorialDir
()) +
'/io/'
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file_1 =
TFile
(path+
"tcontext_1.root"
,
"recreate"
)
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file_2 =
TFile
(path+
"tcontext_2.root"
,
"recreate"
)
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print(
"Current directory: '{}'.\n"
.
format
(
ROOT.gDirectory.GetName
()))
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# Changing directory into another file can be safely done through a TContext
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# context manager.
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with
TDirectory.TContext
(file_1):
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# Inside the statement, the current directory is file_1
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print(
"Current directory: '{}'.\n"
.
format
(
ROOT.gDirectory.GetName
()))
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histo_1 =
ROOT.TH1F
(
"histo_1"
,
"histo_1"
, 10, 0, 10)
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file_1.WriteObject
(histo_1,
"my_histogram"
)
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# After the context, the current directory is restored back to file_2. Also, the
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# two files are kept open. This means that objects read, written or modified
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# inside the context are still available afterwards.
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print(
"Current directory: '{}'.\n"
.
format
(
ROOT.gDirectory.GetName
()))
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if
file_1.IsOpen
()
and
file_2.IsOpen
():
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print(
"'{}' and '{}' are open.\n"
.
format
(
file_1.GetName
(),
file_2.GetName
()))
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# TContext and TFile context managers can also be used in conjunction, allowing
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# for safely:
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# - Opening a file, creating, modifying, writing and reading objects in it.
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# - Closing the file, storing it on disk.
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# - Restoring the previous value of gDirectory to the latest file opened before
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# this context, rather than to the global ROOT.gROOT
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# Remember that the TContext must be initialized before the TFile, otherwise the
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# current directory would already be set to the file opened for this context.
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with
TDirectory.TContext
(),
TFile
(path+
"tcontext_3.root"
,
"recreate"
)
as
f:
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print(
"Current directory: '{}'.\n"
.
format
(
ROOT.gDirectory.GetName
()))
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histo_2 =
ROOT.TH1F
(
"histo_2"
,
"histo_2"
, 10, 0, 10)
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f.WriteObject
(histo_2,
"another_histogram"
)
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print(
"Current directory: '{}'.\n"
.
format
(
ROOT.gDirectory.GetName
()))
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# Cleanup the files created for this tutorial
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file_1.Close
();
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file_2.Close
();
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for
i
in
range
(1, 4):
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os.remove
(path+
"tcontext_{}.root"
.
format
(i))
TRangeDynCast
ROOT::Detail::TRangeCast< T, true > TRangeDynCast
TRangeDynCast is an adapter class that allows the typed iteration through a TCollection.
Definition
TCollection.h:358
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
ROOT::Detail::TRangeCast
Definition
TCollection.h:311
TDirectory::TContext
TDirectory::TContext keeps track and restore the current directory.
Definition
TDirectory.h:89
TFile
A ROOT file is an on-disk file, usually with extension .root, that stores objects in a file-system-li...
Definition
TFile.h:131
tutorials
io
tcontext_context_manager.py
ROOT v6-36 - Reference Guide Generated on Thu Aug 21 2025 04:30:47 (GVA Time) using Doxygen 1.10.0