python argparse: How can I display help automatically on error?

Question

Currently when I enter invalid options or omit positional arguments, argparse kicks me back to the prompt and displays the usage for my app. This is ok, but I would rather automatically display the full help listing (that explains the options, etc) than require the user to type

./myscript.py -h

Thanks!

Jamie

Answer 1

To print help you might want to use: print_help function on ArgumentParser instance

parser = argparse.ArgumentParser() (...) parser.print_help() 

To print help message on error you need to create own subclass of ArgumentParser instance, that overrides error() method. For example like that:

class MyParser(argparse.ArgumentParser):     def error(self, message):       sys.stderr.write('error: %s\n' % message)       self.print_help()       sys.exit(2) 

When this parser encounters unparseable argument line it will print help.