Merged revisions 83675 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/branches/py3k

........
  r83675 | r.david.murray | 2010-08-03 13:56:09 -0400 (Tue, 03 Aug 2010) | 12 lines

  #9444: use first of prefix_chars for help opt instead of raising error

  An argparse option parser created with a prefix_chars that did not
  include a '-' would happily add -h and --help options, and then throw
  an error when it tried to format the help because the - was an invalid
  prefix character.  This patch makes it use the first character of
  prefix_chars as the character for the help options if and only if '-'
  is not one of the valid prefix_chars.

  Fix by Theodore Turocy, unit tests by Catherine Devlin.
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diff --git a/Lib/argparse.py b/Lib/argparse.py
index f9279aa..654ac48 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1563,13 +1563,16 @@
 
         # add help and version arguments if necessary
         # (using explicit default to override global argument_default)
+        default_prefix = '-' if '-' in prefix_chars else prefix_chars[0]
         if self.add_help:
             self.add_argument(
-                '-h', '--help', action='help', default=SUPPRESS,
+                default_prefix+'h', default_prefix*2+'help',
+                action='help', default=SUPPRESS,
                 help=_('show this help message and exit'))
         if self.version:
             self.add_argument(
-                '-v', '--version', action='version', default=SUPPRESS,
+                default_prefix+'v', default_prefix*2+'version',
+                action='version', default=SUPPRESS,
                 version=self.version,
                 help=_("show program's version number and exit"))