Check if a directory argument is writeable or readable.

argparse-dir-arg.py

from os.path import isdir, realpath
import argparse
import os

class ReadableDirectoryAction(argparse.Action):
    def __call__(self, parser, namespace, values, option_string=None):
        prospective_dir = values

        if not isdir(prospective_dir):
            raise argparse.ArgumentTypeError('%s is not a valid directory' % (
                prospective_dir,
            ))

        if os.access(prospective_dir, os.R_OK):
            setattr(namespace, self.dest, realpath(prospective_dir))
            return

        raise argparse.ArgumentTypeError('%s is not a readable directory' % (
            prospective_dir,
        ))


class WritableDirectoryAction(argparse.Action):
    def __call__(self, parser, namespace, values, option_string=None):
        prospective_dir = values

        if not isdir(prospective_dir):
            raise argparse.ArgumentTypeError('%s is not a valid directory' % (
                prospective_dir,
            ))

        if os.access(prospective_dir, os.W_OK):
            setattr(namespace, self.dest, realpath(prospective_dir))
            return

        raise argparse.ArgumentTypeError('%s is not a readable directory' % (
            prospective_dir,
        ))


if __name__ == '__main__':
    parser = argparse.ArgumentParser()

    parser.add_argument('search_path',
                        metavar='SEARCH_PATH',
                        action=ReadableDirectoryAction)
    parser.add_argument('out_dir',
                        metavar='OUT_DIR',
                        action=WritableDirectoryAction)
    parser.add_argument('-v',
                        '--verbose',
                        action='store_true')

There is a typo in the WritableDirectoryAction: '%s is not a readable directory' should be '%s is not a writeable directory'