'Prepares arguments by:
- removing placeholder and moving arguments after it to beginning,
we need this to distinguish arguments from `command` with ours;
- adding `--` before `command`, so our parse would ignore arguments
of `command`.'

def _prepare_arguments(self, argv):

    if (ARGUMENT_PLACEHOLDER in argv):
        index = argv.index(ARGUMENT_PLACEHOLDER)
        return ((argv[(index + 1):] + ['--']) + argv[:index])
    elif (argv and (not argv[0].startswith('-')) and (argv[0] != '--')):
        return (['--'] + argv)
    else:
        return argv
