def check_module(mod_name):
    """Calls sys.exit() if the module *mod_name* is not found."""
    # Special cases #
    if mod_name in module_name: mod_name = module_name[mod_name]
    # Use a try except block #
    try:
        __import__(mod_name)
    except ImportError as e:
        if str(e) != 'No module named %s' % mod_name: raise e
        print 'You do not seem to have the "%s" package properly installed.' \
              ' Either you never installed it or your $PYTHONPATH is not set up correctly.' \
              ' For more instructions see the README file. (%s)' % (mod_name, e)
        sys.exit()