Tim Peters discovered a bug in the Python-supplied getopt():

gvanrossum · gvanrossum · commit 2adac0a6377c · 1999-09-13T13:45:32.000Z
it doesn't recognize a lone dash as a non-flag argument.
Now it does.
diff --git a/Python/getopt.c b/Python/getopt.c
@@ -55,7 +55,8 @@ int getopt( int argc, char *const *argv, const char *optstring )
 
 	if (*opt_ptr == '\0') {
 
-		if (optind >= argc || argv[optind][0] != '-')
+		if (optind >= argc || argv[optind][0] != '-' ||
+		    argv[optind][1] == '\0' /* lone dash */ )
 			return -1;
 
 		else if (strcmp(argv[optind], "--") == 0) {
