How can I automatically display the help on command line arguments 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

see also this SO question for more info: [http://stackoverflow.com/questions/4042452][1] [1]: http://stackoverflow.com/questions/4042452 — jpoppe, Feb 21 '12 at 09:19

score 34 · Answer 1 · edited Apr 26 '23 at 18:24

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:

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

and then use it:

parser = MyParser()

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

score 17 · Accepted Answer · edited Jul 31 '13 at 05:21

17

This thread over at Google groups has the following code snippet which seems to do the trick (modified slightly).

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

edited Jul 31 '13 at 05:21

Mike T

41,085
18
152
203

answered Sep 03 '10 at 15:13

7

Wouldn't it make sense to use `self.print_help(sys.stderr)` here? – hans_meine Nov 24 '14 at 13:31
1

If it's not entirely clear, you should use `DefaultHelpParser` instead of how you usually use `argparse.ArgumentParser` after creating this class – Omer Tuchfeld Mar 05 '19 at 09:51

score 4 · Answer 3 · answered Apr 16 '20 at 21:27

4

I just fixed this same problem myself using the following syntax:

parser = ArgumentParser()
... add arguments ...
parser.usage = parser.format_help()
args = parser.parse_args()

answered Apr 16 '20 at 21:27

infinitesteps

411
3
5

1

The simplicity is enticing, but note that it makes '-h' print the help info twice – Emerson Peters Aug 29 '22 at 22:02

Roger Dahl · Answer 4 · 2019-11-07T07:57:25.563

2

Suppress printing of usage with usage=argparse.SUPPRESS. Then catch the SystemExit exception that ArgumentParser raises on error, print the help, and exit by raising the exception again.

parser = argparse.ArgumentParser(usage=argparse.SUPPRESS)
parser.add_argument(...)
try:
    args = parser.parse_args()
except SystemExit:
    parser.print_help()
    raise

edited Nov 07 '19 at 07:57

answered Nov 07 '19 at 05:24

Roger Dahl

15,132
8
62
82

@GerhardBarnard Read :) – Roger Dahl Nov 27 '19 at 15:27
Now when you invoke the program with `-h`, it prints the help twice. – nisetama Aug 04 '22 at 18:51
1

I wanted to print both the usage and the help message, so I removed the `usage=argparse.SUPPRESS` option when I created the parser object, but I added `arp.usage=argparse.SUPPRESS` on the first line after `except SystemExit:` so the usage isn't printed twice. – nisetama Aug 04 '22 at 18:52

Kassi · Answer 5 · 2020-03-17T19:11:48.467

You, also, can print help without using a class or exception:

def _error(parser):
    def wrapper(interceptor):
        parser.print_help()

        sys.exit(-1)

    return wrapper

def _args_get(args=sys.argv[1:]):
    parser = argparser.ArgumentParser()

    parser.error = _error(parser)

    parser.add_argument(...)
    ...

. Just wrap ArgumentParser.error function in your and intercept message argument. I answered, there, earlier:

https://stackoverflow.com/a/60714163/10152015

How can I automatically display the help on command line arguments error?

5 Answers5

Linked

Related