PyROOT tutorial numberEntry.py broken

[jblomer]

• Checked for duplicates

Describe the bug

The tutorial does not start but prints a backtrace:

Traceback (most recent call last):
  File "/home/jakob/Documents/CERN/ROOT/ntuple/install-git/tutorials/pyroot/numberEntry.py", line 51, in <module>
    window = pMyMainFrame( gClient.GetRoot(), 50, 50 )
  File "/home/jakob/Documents/CERN/ROOT/ntuple/install-git/tutorials/pyroot/numberEntry.py", line 25, in __init__
    self.fLabelDispatch = TPyDispatcher( self.DoSetlabel )
NameError: name 'TPyDispatcher' is not defined

Expected behavior

The tutorial should run

To Reproduce

cd $ROOTSYS/tutorials/pyroot
python -i numberEntry.py

Setup

Compiled from latest ROOT sources / Arch Linux

Additional context

See ROOT forum

[vepadulano]

Indeed TPyDispatcher is present in ROOT:

vpadulan@fedorathinkpad-T550 [~]: python
Python 3.8.7 (default, Jan 20 2021, 00:00:00) 
[GCC 10.2.1 20201125 (Red Hat 10.2.1-9)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import ROOT
>>> ROOT.TPyDispatcher
<class cppyy.gbl.TPyDispatcher at 0x55b264067990>

But in the tutorial numberEntry.py the ROOT objects are imported via from ROOT import * which somehow doesn't import TPyDispatcher in the python session. Indeed, changing that line with import ROOT and then explicitly instantiating ROOT.TPyDispatcher solves this issue

Now in general from <package> import * is discouraged so I would change the tutorial, but it is true that ROOT also has its own machinery to decide which names are imported into the namespace in this case and I still don't know why TPyDispatcher is not loaded along all the other classes