Composable Python argparse actions

composable_actions.py

import argparse

def compose_actions(*actions):
    """Compose many argparse actions into one callable action.

    Args:
        *actions: The actions to compose.

    Returns:
        argparse.Action: Composed action.
    """
    class ComposableAction(argparse.Action):
        def __call__(self, parser, namespace, values, option_string=None):
            for action in actions:
                action(option_string, self.dest).__call__(parser,
                                                          namespace,
                                                          values,
                                                          option_string)
    return ComposableAction

example.py

import argparse
import simplejson as json
import os

from composable_actions import compose_actions


class ReadableFileAction(argparse.Action):
    """Argparse hook to check for readable file within directory."""

    def __call__(self, parser, namespace, values, option_string=None):
        """Readble file action callable.

        Raises:
            parser.error: The file is not readable.
        """
        if not values:
            return
        prospective_file = values
        prospective_dir = os.path.dirname(os.path.abspath(prospective_file))
        if not os.path.isdir(prospective_dir):
            raise parser.error(
                '{} is not a valid file path'.format(prospective_file)
            )
        if os.access(prospective_dir + '/' + prospective_file, os.R_OK):
            setattr(namespace, self.dest, prospective_file)
            return
        raise parser.error('{} isnt a readable file'.format(prospective_file))


class LoadFileToJsonAction(argparse.Action):
    """Argparse hook to read JSON file and load into Python dictionary."""

    def __call__(self, parser, namespace, values, option_string=None):
        """Load file to JSON Action.

        Raises:
            parser.error: invalid JSON.
        """
        with open(values, 'r') as file:
            data = file.read()
        try:
            setattr(parser, self.dest, json.loads(data))
        except json.scanner.JSONDecodeError:
            parser.error('invalid JSON in {}'.format(values))


parser = argparse.ArgumentParser()
parser.add_argument('--json-file', dest='data', action=compose_actions(ReadableFileAction, LoadToJsonAction))