How to use the plac.Interpreter function in plac

def test():
    with plac.Interpreter(ishelve.main) as i:
        i.check('.clear', 'cleared the shelve')
        i.check('a=1', 'setting a=1')
        i.check('a', '1')
        i.check('.delete=a', 'deleted a')
        i.check('a', 'a: not found')

def submit_tasks(self):
        npoints = math.ceil(self.npoints / self.n_cpu)
        self.i = plac.Interpreter(self).__enter__()
        return [self.i.submit('calc_pi %d' % npoints)
                for _ in range(self.n_cpu)]

baseparser = plac.parser_from(main)
    if fname is None:
        baseparser.print_help()
    elif sys.argv[1] == fname:  # script mode
        plactool = plac.import_main(fname)
        plactool.prog = os.path.basename(sys.argv[0]) + ' ' + fname
        out = plac.call(plactool, sys.argv[2:], eager=False)
        if plac.iterable(out):
            for output in out:
                print(output)
        else:
            print(out)
    elif interactive or multiline or serve:
        plactool = plac.import_main(fname, *extra)
        plactool.prog = ''
        i = plac.Interpreter(plactool)
        if interactive:
            i.interact(verbose=verbose)
        elif multiline:
            i.multiline(verbose=verbose)
        elif serve:
            i.start_server(serve)
    elif batch:
        run((fname,) + extra, 'execute', verbose)
    elif test:
        run((fname,) + extra, 'doctest', verbose)
        print('run %s plac test(s)' % (len(extra) + 1))
    else:
        baseparser.print_usage()
main.add_help = False

def run(fnames, cmd, verbose):
    "Run batch scripts and tests"
    for fname in fnames:
        with open(fname) as f:
            lines = list(f)
        if not lines[0].startswith('#!'):
            sys.exit('Missing or incorrect shebang line!')
        firstline = lines[0][2:]  # strip the shebang
        init_args = shlex.split(firstline)
        tool = plac.import_main(*init_args)
        command = getattr(plac.Interpreter(tool), cmd)  # doctest or execute
        if verbose:
            sys.stdout.write('Running %s with %s' % (fname, firstline))
        command(lines[1:], verbose=verbose)