[Python] Python argparse: 'usage' text showing formatter object when using custom formatter

I got a script with a list of arguments defined with argparse. Because I want to have bullet points and line breaks in the help text, I added a custom formatter. That works like a charm but the problem now is that the default 'usage' text in the help, now shows the formatter object:

usage: <__main__.MyFormatter object at 0x7f30cc163c70> [-h] {list,add,remove} ...


If I remove the custom formatter, then the 'usage' is as expected:

usage: test.py [-h] {list,add,remove} ...


And I can't understand why and how to fix it.

Here's a stripped down version of my script (test.py):

import argparse
class MyFormatter(argparse.ArgumentDefaultsHelpFormatter):
def __init__(self,
prog,
indent_increment=2,
max_help_position=30,
width=None):
super().__init__(self,
indent_increment=indent_increment,
max_help_position=max_help_position,
width=width)
def _split_lines(self, text, width):
"""
If the text starts with 'S|', remove the prefix, split the text into lines at the new line '\n'
and maintain spaces. Otherwise, uses the default splitting behavior of ArgumentDefaultsHelpFormatter.
"""
if text.startswith('S|'):
text = text[2:].strip().splitlines()
import textwrap
out = []
for line in text:
out.extend(textwrap.wrap(line, width))
return out
return argparse.ArgumentDefaultsHelpFormatter._split_lines(self, text, width)

parser = argparse.ArgumentParser(description="This script will do a bunch of stuff",
formatter_class=MyFormatter)
parser.set_defaults(func=lambda args: parser.print_help())
subparsers = parser.add_subparsers()

parser_list = subparsers.add_parser("list", help="Show a list of things", formatter_class=MyFormatter)

parser_add = subparsers.add_parser("add", help="Add item to the list", formatter_class=MyFormatter)
parser_add.add_argument("item", type=str, help="Item to add to the list")

parser_remove = subparsers.add_parser("remove", help="Remove item from the list", formatter_class=MyFormatter)
parser_remove.add_argument("item", type=str, help="Item to remove from the list")

args = parser.parse_args()



I know I can add my own usage message with the 'usage=' argument, but I'm more trying to understand why using the custom formatter breaks the usage text?

PS. using Python 3.12

Continue reading...