#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.

2 files changed, 5 insertions, 0 deletions

diff --git a/Misc/ACKS b/Misc/ACKS
index 480e35d..0347f67 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -802,6 +802,7 @@ John Tromp
 Jason Trowbridge
 Anthony Tuininga
 Stephen Turner
+Theodore Turocy
 Bill Tutt
 Doobee R. Tzeck
 Eren Türkay
diff --git a/Misc/NEWS b/Misc/NEWS
index a1f07f7..1780e5d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -35,6 +35,10 @@ Extensions
 Library
 -------
 
+- Issue #9444: Argparse now uses the first element of prefix_chars as
+  the option character for the added 'h/help' option if prefix_chars
+  does not contain a '-', instead of raising an error.
+
 - Issue #7372: Fix pstats regression when stripping paths from profile
   data generated with the profile module.