The parser starts out with 2 argument groups, the usual positional and optionals. The -h help is added to optionals. When you do add_argument_group, a group is created (and returned to you). It is also appended to the parser._action_groups list.
When you ask for help (-h) parser.format_help() is called (you can do that as well in testing). Look for that method in argparse.py. That sets up the help message, and one step is:
# positionals, optionals and user-defined groups for action_group in self._action_groups: formatter.start_section(action_group.title) formatter.add_text(action_group.description) formatter.add_arguments(action_group._group_actions) formatter.end_section()
So if we reorder the items in the parser._action_groups list, we will reorder the groups in the display. Since this is the only use of _action_groups it should be safe and easy. But some people aren't allowed to peak under the covers (look or change ._ attributes).
The proposed solution(s) is to make your own groups in the order you want to see them, and make sure that the default groups are empty (the add_help=False parameter). That's the only way to do this if you stick with the public API.
Demo:
import argparse parser = argparse.ArgumentParser() parser.add_argument('foo') g1 = parser.add_argument_group('REQUIRED') g1.add_argument('--bar', required=True) g1.add_argument('baz', nargs=2) print(parser._action_groups) print([group.title for group in parser._action_groups]) print(parser.format_help()) parser._action_groups.reverse() # easy inplace change parser.print_help()
Run result:
1504:~/mypy$ python stack39047075.py
_actions_group list and titles:
[<argparse._ArgumentGroup object at 0xb7247fac>, <argparse._ArgumentGroup object at 0xb7247f6c>, <argparse._ArgumentGroup object at 0xb721de0c>] ['positional arguments', 'optional arguments', 'REQUIRED']
default help:
usage: stack39047075.py [-h] --bar BAR foo baz baz positional arguments: foo optional arguments: -h, --help show this help message and exit REQUIRED: --bar BAR baz
after reverse:
usage: stack39047075.py [-h] --bar BAR foo baz baz REQUIRED: --bar BAR baz optional arguments: -h, --help show this help message and exit positional arguments: foo 1504:~/mypy$
Another way to implement this is to define a ArgumentParser subclass with a new format_help method. In that method reorder the list used in that for action_group... loop.
