bpo-37785: Fix xgettext warning in argparse (GH-15161)

Author: kulikjak

Lib/argparse.py

@@ -1214,8 +1214,9 @@ def __call__(self, string):
             return open(string, self._mode, self._bufsize, self._encoding,
                         self._errors)
         except OSError as e:
-            message = _("can't open '%s': %s")
-            raise ArgumentTypeError(message % (string, e))
+            args = {'filename': string, 'error': e}
+            message = _("can't open '%(filename)s': %(error)s")
+            raise ArgumentTypeError(message % args)
 
     def __repr__(self):
         args = self._mode, self._bufsize

Misc/NEWS.d/next/Library/2019-08-07-14-49-22.bpo-37785.y7OlT8.rst

@@ -0,0 +1 @@
+Fix xgettext warnings in :mod:`argparse`.