bpo-14156: Make argparse.FileType work correctly for binary file modes when argument is '-' (GH-13165)

Also made modes containing 'a' or 'x' act the same as a mode containing 'w' when argument is '-'
(so 'a'/'x' return sys.stdout like 'w', and 'ab'/'xb' return sys.stdout.buffer like 'wb').
(cherry picked from commit eafec26ae5327bb23b6dace2650b074c3327dfa0)

Co-authored-by: MojoVampire <shadowranger+github@gmail.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/Lib/argparse.py b/Lib/argparse.py
index b71a6703c3..2c0dd853a5 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -726,7 +726,7 @@ def _get_action_name(argument):
     if argument is None:
         return None
     elif argument.option_strings:
-        return  '/'.join(argument.option_strings)
+        return '/'.join(argument.option_strings)
     elif argument.metavar not in (None, SUPPRESS):
         return argument.metavar
     elif argument.dest not in (None, SUPPRESS):
@@ -1256,9 +1256,9 @@ class FileType(object):
         # the special argument "-" means sys.std{in,out}
         if string == '-':
             if 'r' in self._mode:
-                return _sys.stdin
-            elif 'w' in self._mode:
-                return _sys.stdout
+                return _sys.stdin.buffer if 'b' in self._mode else _sys.stdin
+            elif any(c in self._mode for c in 'wax'):
+                return _sys.stdout.buffer if 'b' in self._mode else _sys.stdout
             else:
                 msg = _('argument "-" with mode %r') % self._mode
                 raise ValueError(msg)