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PyROOT installation

The Processor for Analysing XENON (PAX) can use ROOT (http://root.cern.ch/drupal/) as a processed data output format. If you want to use this output format, you'll first have to install pyROOT (a Python module to interact with ROOT classes) in the latest version of Python (3.4). This installation document shows the steps needed to do this correctly in an virtual environment on Ubuntu 14.

Installation

We assume installation on Ubuntu 14 desktop with python3.4 pre-installed.

  • To install virualenv with py3.4 run:

    sudo apt-get install python-pip
sudo pip install virtualenv
virtualenv -p /usr/bin/python3.4 $HOME/env/py34
source ~/env/py34/bin/activate

Check that python3.4 starts when typing 'python' after activating the virtualenv. The virtualenv can be exited by typing 'deactivate'.

To get ROOT ready for compilation:

  • Download the latest root: http://root.cern.ch/drupal/content/downloading-root

  • Unpack and install dependencies with the command from: http://root.cern.ch/drupal/content/build-prerequisites:

    mkdir ~/env/py34/src
cd ~/env/py34/src
gzip -dc root_<version>.source.tar.gz | tar -xf -
sudo apt-get install git dpkg-dev make g++ gcc binutils libx11-dev libxpm-dev libxft-dev libxext-dev

  • Search for the files Python.h and libpython3.4.so:

    sudo updatedb
locate Python.h
locate libpython3.4.so

  • If they are not found run:

    sudo apt-get install python3.4-dev

  • Now go to the root directory and set configure to the locations of the found files of the correct python version.:

    ./configure --enable-python --with-python-incdir=/usr/include/python3.4m --with-python-libdir=/usr/lib/python3.4/config-3.4m-x86_64-linux-gnu

where the Python include directory should point to the directory containing the Python.h file, and the library directory should contain libpython.x.y.[so][.dll], where 'x' and 'y' are the major and minor version number of Python, respectively. Note that at the end of the configuration, the list of enabled features is printed: make sure that 'python' is listed among them. If you do not specify the inc and lib directories configure will try to use the environment variable $PYTHONDIR or alternatively will look in the standard locations.

  • The output should now include:

    Checking for Python.h ... /usr/include/python3.4m
Checking for python3.4, libpython3.4, libpython, python, or Python ... /usr/lib/

  • Compile ROOT:

    make

TIP: When running the command make above, one can multi thread the build by doing make -jN for an N-core machine. For example, in a four core laptop, one could do make -j4. The ROOT build should be successful

  • Check that the PyROOT module was build correctly by looking for ROOT.py and libPyROOT.so:

    sudo updatedb
locate ROOT.py
locate libPyROOT.so

  • Set this root as source for the env:

    echo source bin/thisroot.sh >> ~/env/py34/bin/activate

The last part of the pyROOT install deals with the ROOT.py file. You can either convert it yourself or copy the file provided in pax/travis.

To use the provided ROOT.py from PAX.

  • Copy the file to the proper directory:

    #Using ROOT v5
cp pax/travis/modified_ROOT_v5.34.25.py ~/env/py34/src/root/lib/ROOT.py

#Using ROOT v6
cp pax/travis/modified_ROOT_v6.02.05.py ~/env/py34/src/root/lib/ROOT.py

To manually convert ROOT.py.

  • Convert the code in ROOT.py from python 2 to python 3 with 2to3:

    2to3 -w ~/env/py34/src/root/lib/ROOT.py

  • Some tweaking of ROOT.py is required, comment out the following lines in ROOT.py (on lines 355, 542-544), (this rather ad hoc modification disables the backwards compatibility, but since we are using python 3 this is not needed):

    builtins.__import__ = _importhook

# special case for cout (backwards compatibility)
if hasattr( std, '__1' ):
  self.__dict__[ 'cout' ] = getattr( std, '__1' ).cout

  • ROOT.py also has a cleanup() function that is called when PAX shuts down, since we have changed the behaviour of ROOT.py this function causes errors. Bypass it by putting a return statement after its definition (yes, this is not good practise and we are looking for a better solution):

    def cleanup():
    return

Start python and check that "import ROOT" works. If so happy programming.

Now every time you want to use PyROOT 3.4 activate the virtualenv::

source ~/env/py34/bin/activate