<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def extant_file(path):
 """ Check if file exists with argparse """

    if not os.path.exists(path):
        raise argparse.ArgumentTypeError("{} does not exist".format(path))
    return path