According to Craig H Rowland, openbsd2 is yet another BSD variant that

gvanrossum · gvanrossum · commit 5274c336f5c3 · 1999-12-06T14:51:05.000Z
uses the BSD version of the lock structure.  Sigh, @!%$.
diff --git a/Lib/posixfile.py b/Lib/posixfile.py
@@ -178,6 +178,7 @@ def lock(self, how, *args):
         # additions for AIX by Vladimir.Marangozov@imag.fr
         import sys, os
         if sys.platform in ('netbsd1',
+                            'openbsd2',
                             'freebsd2', 'freebsd3',
                             'bsdos2', 'bsdos3', 'bsdos4'):
             flock = struct.pack('lxxxxlxxxxlhh', \
@@ -193,6 +194,7 @@ def lock(self, how, *args):
 
         if '?' in how:
             if sys.platform in ('netbsd1',
+                                'openbsd2',
                                 'freebsd2', 'freebsd3',
                                 'bsdos2', 'bsdos3', 'bsdos4'):
                 l_start, l_len, l_pid, l_type, l_whence = \
