code: def check_installation(cur_file):
    
    cur_dir = os.path.split(os.path.dirname(os.path.abspath(cur_file)))[0]
    ch_dir = os.path.split(cleverhans.__path__[0])[0]
    if cur_dir != ch_dir:
      warnings.warn("It appears that you have at least two versions of "
                    "cleverhans installed, one at %s and one at"
                    " %s. You are running the tutorial script from the "
                    "former but python imported the library module from the "
                    "latter. This may cause errors, for example if the tutorial"
                    " version is newer than the library version and attempts to"
                    " call new features." % (cur_dir, ch_dir))
docs: Warn user if running cleverhans from a different directory than tutorial.