utils.py

import argparse
import os


class IsReadableDir(argparse.Action):
    def __call__(self, parser, namespace, values, option_string=None):
        prospective_dir = values
        if not os.path.isdir(prospective_dir):
            raise argparse.ArgumentTypeError(
                "{0} is not a valid path".format(prospective_dir)
            )
        if os.access(prospective_dir, os.R_OK):
            setattr(namespace, self.dest, prospective_dir)
        else:
            raise argparse.ArgumentTypeError(
                "{0} is not a readable directory".format(prospective_dir)
            )


class IsValidFile(argparse.Action):
    def __call__(self, parser, namespace, values, option_string=None):
        prospective_file = values
        if not os.path.exists(prospective_file):
            raise argparse.ArgumentTypeError(
                "{0} is not a valid file".format(prospective_file)
            )
        else:
            setattr(namespace, self.dest, prospective_file)