whether I edit the mesh's normal in python console, or even if I manually reverse the order of the vertices in python.

how do I get my changes to the mesh data in python to take effect on the actual blender model/mesh/scene/whatever?

here's a video to illustrate my problem:
bcaptain.net/blender-normals.mpeg

and here's the code I wrote to reverse a quad's vertex order:

Code:

sce = bpy.context.scene #sce = bpy.data.scenes.active ob = sce.objects.active mesh = bpy.context.active_object.to_mesh(bpy.context.scene, True, 'PREVIEW') # ** show current normal mesh.polygons[0].normal # ** flip vertices of a quad tmp=mesh.polygons[0].vertices[0] mesh.polygons[0].vertices[0]=mesh.polygons[0].vertices[3] mesh.polygons[0].vertices[3]=tmp tmp=mesh.polygons[0].vertices[1] mesh.polygons[0].vertices[1]=mesh.polygons[0].vertices[2] mesh.polygons[0].vertices[2]=tmp mesh.update( calc_edges=True ) # ** show new normal mesh.polygons[0].normal

This seems like a pretty simple thing, somebody must have an answer to this.

After some thinking, I presume that I am not editing the mesh data directly, but instead a copy.

mesh = bpy.context.active_object.to_mesh(bpy.context.scene, True, 'PREVIEW')

how to edit the mesh directly.. that is the question!

there can be issues with the "old" api, you should try the bmesh module. It has a special function to update normals:

http://www.blender.org/documentation/blender_python_api_2_65_release/bmesh.types.html#bmesh.types.BMesh.normal_update

but if you really wanna use the old api, switch from edit to object mode, apply changes, then switch back. This may last a while for complex models and eat memory, but otherwise changes are likely ignored (in edit mode)
_________________
I'm sitting, waiting, wishing, building Blender in superstition...

CoDEmanX wrote:

there can be issues with the "old" api, you should try the bmesh module. It has a special function to update normals: http://www.blender.org/documentation/blender_python_api_2_65_release/bmesh.types.html#bmesh.types.BMesh.normal_update but if you really wanna use the old api, switch from edit to object mode, apply changes, then switch back. This may last a while for complex models and eat memory, but otherwise changes are likely ignored (in edit mode)

I didn't realize there was an "old" api. I wrote an export script using roughly the same python code and it took a while to wade through what was "old blender" and what was "new blender" because 2.63 is so new. But... I guess I've got some homework to do.