python · DiPaolo · Jan 9, 2021 · Jan 15, 2021 · Jan 15, 2021
@@ -259,13 +259,12 @@ def add_argument(self, action):
 
             # find all invocations
             get_invocation = self._format_action_invocation
-            invocations = [get_invocation(action)]
+            invocation_lengths = [len(get_invocation(action)) + self._current_indent]
             for subaction in self._iter_indented_subactions(action):
-                invocations.append(get_invocation(subaction))
+                invocation_lengths.append(len(get_invocation(subaction)) + self._current_indent)
 
             # update the maximum item length
-            invocation_length = max(map(len, invocations))
-            action_length = invocation_length + self._current_indent
+            action_length = max(invocation_lengths)
             self._action_max_length = max(self._action_max_length,
                                           action_length)
 

@@ -4412,6 +4412,49 @@ def custom_type(string):
     version = ''
 
 
+class TestHelpUsageLongSubparserCommand(TestCase):
+    """Test that long command in subparser is displayed correctly in help
+
+    The test was added for https://bugs.python.org/issue42875
+    """
+
+    def setUp(self):
+        super().setUp()
+        self.main_program = os.path.basename(sys.argv[0])
+
+    def test_parent_help(self):
+        parent_parser = argparse.ArgumentParser(
+            add_help=False, formatter_class=lambda prog: argparse.RawTextHelpFormatter(prog, max_help_position=50))
+
+        main_parser = argparse.ArgumentParser(
+            formatter_class=lambda prog: argparse.RawTextHelpFormatter(prog, max_help_position=50))
+        cmd_subparsers = main_parser.add_subparsers(title="commands", metavar='CMD', help='command to use')
+
+        cmd_parser = cmd_subparsers.add_parser("add", help="add something", parents=[parent_parser])
+        cmd_parser.add_subparsers(title="action", dest="action_command")
+
+        cmd_parser2 = cmd_subparsers.add_parser("remove", help="remove something", parents=[parent_parser])
+        cmd_parser2.add_subparsers(title="action", dest="action_command")
+
+        cmd_subparsers.add_parser("a-very-long-command", help="command that does something", parents=[parent_parser])
+
+        parser_help = main_parser.format_help()
+
+        progname = self.main_program
+        self.assertEqual(parser_help, textwrap.dedent('''\
+            usage: {}{}[-h] CMD ...
+
+            options:
+              -h, --help             show this help message and exit
+
+            commands:
+              CMD                    command to use
+                add                  add something
+                remove               remove something
+                a-very-long-command  command that does something
+        '''.format(progname, ' ' if progname else '')))
+
+
 # =====================================
 # Optional/Positional constructor tests
 # =====================================

diff --git a/Misc/NEWS.d/next/Library/2021-01-15-18-09-27.bpo-42875.puKGeU.rst b/Misc/NEWS.d/next/Library/2021-01-15-18-09-27.bpo-42875.puKGeU.rst
@@ -0,0 +1 @@
+Fixed incorrect indentation in command line help generated by argparse: in case of usage a long command along with max_help_position which is more than the length of the command, the command's help was incorrectly started on the new line.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Fixed incorrect indentation in command line help generated by argparse: in case of usage a long command along with max_help_position which is more than the length of the command, the command's help was incorrectly started on the new line.