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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def extant_item(arg, arg_type):
 """Determine if parser argument is an existing file or directory. This technique comes from http://stackoverflow.com/a/11541450/95592 and from http://stackoverflow.com/a/11541495/95592 Args: arg: parser argument containing filename to be checked arg_type: string of either "file" or "directory" Returns: If the file exists, return the filename or directory. Raises: If the file does not exist, raise a parser error. """

    if arg_type == "file":
        if not os.path.isfile(arg):
            raise argparse.ArgumentError(
                None,
                "The file {arg} does not exist.".format(arg=arg))
        else:
            # File exists so return the filename
            return arg
    elif arg_type == "directory":
        if not os.path.isdir(arg):
            raise argparse.ArgumentError(
                None,
                "The directory {arg} does not exist.".format(arg=arg))
        else:
            # Directory exists so return the directory name
            return arg