PyAPI: Store PyInstances for ID's

This means once an ID is created,
it will keep using the same PyObject instance.

This has some advantages:
- Avoids unnecessary re-creation of instances on UI poll / redraw.
- Accessing free'd ID's gives an exception instead of crashing.
  (long standing annoyance!, though this only applies to ID's
   and not yet other data that uses the ID's - vertices for eg).
- Allows using instance comparison (a little faster).

Note that the instances won't be kept between undo.

1 files changed, 1 insertions, 0 deletions

diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index 7f92cc9e8bb..6349269440e 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -2221,6 +2221,7 @@ static void direct_link_id(FileData *fd, ID *id)
 		/* this case means the data was written incorrectly, it should not happen */
 		IDP_DirectLinkGroup_OrFree(&id->properties, (fd->flags & FD_FLAGS_SWITCH_ENDIAN), fd);
 	}
+	id->py_instance = NULL;
 }
 
 /* ************ READ CurveMapping *************** */