A wrapper script to try to start Ganga with Python 2.7

launch_ganga

#! /usr/bin/env python
"""
This script will launch Ganga with an appropriate interpreter
"""

from __future__ import print_function

import os
import re
import subprocess
import sys
try:  # py3
    from shlex import quote
except ImportError:  # py2
    from pipes import quote


def get_python(commands, version):
    """
    Args:
        commands: a list of python interpreters
        version: a 2-element version tuple

    Returns:
        str: the first interpreter from ``commands`` that fulfils ``version``
    """
    version_match = re.compile(r'(\d*)\.(\d*)\.(\d*)')

    for command in commands:
        try:
            p = subprocess.Popen(' '.join([command, '--version']), shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
            stdout, stderr = p.communicate()
        except OSError:
            continue  # Command not found
        v = version_match.search(stdout)
        if not v:
            continue  # Could not match version

        if int(v.group(1)) == version[0] and int(v.group(2)) == version[1]:
            return command

wanted_version = (2, 7)  # The required version of Python to run

ganga_script = os.path.join(os.path.dirname(os.path.realpath(__file__)), 'ganga')  # The application entry_point
args = [quote(arg) for arg in sys.argv[1:]]  # Arguments passed in

if sys.version_info[0] == wanted_version[0] and sys.version_info[1] == wanted_version[1]:
    print('Launching Ganga with this interpreter')
    execfile(ganga_script)
else:
    pythons = (
        'python',  # Try this first to match defaults and virtualenvs
        'python2.7',  # If ``python`` is 2.6 this may exist
        'scl enable python27 -- python',  # Try a RedHat SCL
        '/cvmfs/sft.cern.ch/lcg/external/Python/2.7.4/x86_64-slc6-gcc48-opt/bin/python',
    )

    python = get_python(pythons, wanted_version)

    if python is None:
        print('Could not find a suitable Python interpreter. Tried', pythons)
        exit(1)

    print('Launching Ganga with', python)

    rc = subprocess.call(' '.join([python, ganga_script, args]), shell=True)
    exit(rc)