bpo-26510: Add versionchanged for required arg of add_subparsers (GH-16588)


The `required` argument to `argparse.add_subparsers` was added in GH-3027. This PR specifies the earliest version of Python where it is available.

https://bugs.python.org/issue26510

Automerge-Triggered-By: @merwok
(cherry picked from commit 9e71917e0290972f65711f75510078f799cf0b59)

Co-authored-by: Adam J. Stewart <ajstewart426@gmail.com>
diff --git a/Doc/library/argparse.rst b/Doc/library/argparse.rst
index 56bd641..ee005594 100644
--- a/Doc/library/argparse.rst
+++ b/Doc/library/argparse.rst
@@ -1595,7 +1595,7 @@
      stored; by default ``None`` and no value is stored
 
    * required_ - Whether or not a subcommand must be provided, by default
-     ``False``.
+     ``False`` (added in 3.7)
 
    * help_ - help for sub-parser group in help output, by default ``None``
 
@@ -1751,6 +1751,9 @@
      >>> parser.parse_args(['2', 'frobble'])
      Namespace(subparser_name='2', y='frobble')
 
+   .. versionchanged:: 3.7
+      New *required* keyword argument.
+
 
 FileType objects
 ^^^^^^^^^^^^^^^^