Simple pattern for adding a REPL to argparse-based command line programs

argparse_repl.py

# This came up when I couldn't add dependencies beyond the stdlib for a certain script

import argparse
import sys, os.path

def run(args):
    # Do actual things
    pass

def main():
    parser = argparse.ArgumentParser()
    
    # All the args
    
    parser.add_argument("--interactive", action="store_true", help="Interactive mode")
    
    args = parser.parse_args()
    
    if not args.interactive:
        run(args)
        return
    
    # --Interactive mode--
    
    # First, keep ArgParser from exiting on invalid input
    class InvalidArgs(Exception):
        pass
    def exit(*args, **kwargs):
        raise InvalidArgs
    parser.exit = exit

    # readline adds capabilities to input
    try:
        import readline
    except:
        pass

    print("Enter commands. Use 'help' for info, 'exit' to leave.")
    while True:
        try:
            command = input('> ').strip()
            
            # remove the program name if they typed it
            prog_name = os.path.basename(sys.argv[0])
            command = re.sub(r'^{}\s+'.format(prog_name), '', command)
        except KeyboardInterrupt:
            # Ctrl-c clears the input
            sys.stdout.write('\n')
            continue
        except EOFError:
            # Ctrl-d exits
            sys.stdout.write('\n')
            break

        if command == 'exit':
            break

        if command in ['help', 'h', '?']:
            parser.print_help()
            continue

        try:
            command_args = parser.parse_args(args=command.split())
        except InvalidArgs:
            print('Invalid command')
            continue

        if command_args.interactive:
            # Don't let them get clever
            continue

        run(command_args)