--- xen-4.12.0/tools/pygrub/src/pygrub.orig	2019-04-01 21:25:33.206405995 +0100
+++ xen-4.12.0/tools/pygrub/src/pygrub	2019-04-01 21:27:36.179929105 +0100
@@ -963,5 +963,8 @@
         ostring = format_simple(bootcfg["kernel"], bootcfg["ramdisk"], args, "\0")
 
     sys.stdout.flush()
-    os.write(fd, ostring)
+    if sys.version_info[0] < 3:
+        os.write(fd, ostring)
+    else:
+        os.write(fd, ostring.encode())