commit aaf6fc0982c916cb71d9e0afcd7dda4ba495793b
author Anthony Sottile <asottile@umich.edu> Wed Sep 20 14:35:27 2017 -0700
committer Éric Araujo <merwok@users.noreply.github.com> Wed Sep 20 17:35:27 2017 -0400
tree 09cb0078fade182a8be0a108bb50b57a71156bd9
parent 19e4d9346db7fb65845b98a9cb9caacaaac8a81a

bpo-26510: make argparse subparsers required by default (#3027)

This fixes a regression from Python 2.  To get optional subparsers,
use the new parameter ``add_subparsers(required=False)``.

Patch by Anthony Sottile.

Lib/argparse.py

diff --git a/Lib/argparse.py b/Lib/argparse.py
index d59e645..98bbed0 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1066,6 +1066,7 @@
                  prog,
                  parser_class,
                  dest=SUPPRESS,
+                 required=True,
                  help=None,
                  metavar=None):
 
@@ -1079,6 +1080,7 @@
             dest=dest,
             nargs=PARSER,
             choices=self._name_parser_map,
+            required=required,
             help=help,
             metavar=metavar)