max_help_position is not works in argparse library

[morden2k]

BPO	25297
Files	issue25297.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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assignee = None
closed_at = None
created_at = <Date 2015-10-02.08:55:13.943>
labels = ['library']
title = 'max_help_position is not works in argparse library'
updated_at = <Date 2015-10-03.21:30:55.770>
user = 'https://bugs.python.org/morden2k'

bugs.python.org fields:

activity = <Date 2015-10-03.21:30:55.770>
actor = 'paul.j3'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2015-10-02.08:55:13.943>
creator = 'morden2k'
dependencies = []
files = ['40661']
hgrepos = []
issue_num = 25297
keywords = []
message_count = 5.0
messages = ['252093', '252095', '252144', '252164', '252242']
nosy_count = 2.0
nosy_names = ['paul.j3', 'morden2k']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue25297'
versions = ['Python 2.7']

[morden2k]

Hi colleagues I have the code (max_help_position is 2000):

formatter_class=lambda prog: argparse.HelpFormatter(prog, max_help_position=2000)
parser = argparse.ArgumentParser(formatter_class=formatter_class)


subparsers = parser.add_subparsers(title="Commands", metavar="<command>")

cmd_parser = subparsers.add_parser('long_long_long_long_long_long_long',
                                   help='- jksljdalkjda',
                                   formatter_class=formatter_class)

args = parser.parse_args(['-h'])
print args

Result:

we have

optional arguments:
-h, --help show this help message and exit

Commands:
<command>
long_long_long_long_long_long_long
- jksljdalkjda
small - descr

instead

optional arguments:
-h, --help show this help message and exit

Commands:
<command>
long_long_long_long_long_long_long - jksljdalkjda
small - descr

The code:

class MyFormatter(argparse.HelpFormatter):
    def __init__(self, prog):
        super(MyFormatter, self).__init__(prog, max_help_position=2000, width=2000)
        self._max_help_position = 2000
        self._action_max_length += 4

got same result.

The strings like:

formatter_class = lambda prog: argparse.HelpFormatter(prog,
                  max_help_position=2000, width=2000)

formatter_class = lambda prog: argparse.HelpFormatter(prog,
                  max_help_position=1000, width=2000)

formatter_class = lambda prog: argparse.HelpFormatter(prog,
                  max_help_position=2000, width=1000)

got same result: we always have new line after command.

[morden2k]

Problem also described on http://stackoverflow.com/questions/32888815/

[paulj3]

My testing shows that it's a problem with the subparsers listing. When regular arguments are long, 'max_help_position' works (within limits allowed by 'width').

[paulj3]

There's a bug in the HelpFormatter.add_argument method. It does not take into account the extra indentation of subactions (sub parsers) when calculating self._action_max_length.

The corrected method and a test case is in the attached file.

class MyFormatter(argparse.HelpFormatter):
    """
    Corrected _max_action_length for the indenting of subactions
    """
    def add_argument(self, action):
        if action.help is not argparse.SUPPRESS:

            # find all invocations
            get_invocation = self._format_action_invocation
            invocations = [get_invocation(action)]
            current_indent = self._current_indent
            for subaction in self._iter_indented_subactions(action):
                # compensate for the indent that will be added
                indent_chg = self._current_indent - current_indent
                added_indent = 'x'*indent_chg
                invocations.append(added_indent + get_invocation( subaction) )
            # print('inv', invocations)

            # update the maximum item length
            invocation_length = max([len(s) for s in invocations])
            action_length = invocation_length + self._current_indent
            self._action_max_length = max(self._action_max_length,
                                          action_length)

            # add the item to the list
            self._add_item(self._format_action, [action])

Without this correction self._action_max_length is off by 2 if a subparser has the longest invocation. Normally that wouldn't be an issue since normally subparser names are short and easy to use. But with the 'aliases' that newer argparse allows, the invocation could be longer, and possibly longer than regular arguments.

I haven't passed this correction through test_argparse.py. It also would need a test case or two. I don't think it need a documentation change.

I don't know if this correction will work with the subparser grouping proposed in http://bugs.python.org/issue9341.

[paulj3]

The unittest test_argparse.py has one related test

class TestAddSubparsers
def test_alias_help

has a long enough subparser invocation (with aliases) to produce wrapping with the default 24 max position:

        commands:
          COMMAND
            1 (1alias1, 1alias2)
                                1 help
            2                   2 help

I don't see anything in the test file that tries to vary the max_help_position parameter.