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I have tried the following but the mat is not assigned to any of the faces.

import bpy
import bmesh

Creating a new Mat


mat = bpy.data.materials.new(name="newMat")
mat.diffuse_color = (0.5,0,0.5,1)


Generating a Box


bpy.ops.mesh.primitive_cube_add(size=2,  enter_editmode=True, location=(0, 0, 0))


Resizing and Translating the box


bpy.ops.mesh.select_all(action='SELECT')
bpy.ops.transform.resize(value=(0.5, 1, 1))
bpy.ops.transform.translate(value=(0.5, 0, 0))
bpy.ops.mesh.select_all(action='DESELECT')


Instantiating the bmesh of the Box


obj = bpy.context.edit_object
me = obj.data
bm = bmesh.from_edit_mesh(me)


Selecting just one of the faces


bm.faces[0].select = True


toggle to edit mode


bpy.ops.object.mode_set(mode='EDIT')


make sure face select mode is enabled


bpy.context.tool_settings.mesh_select_mode = [False, False, True]


use second material slot


ob = bpy.context.active_object
ob.active_material_index = 1


assign the material


bpy.ops.object.material_slot_assign()


toggle to object mode


bpy.ops.object.mode_set(mode='OBJECT')

What am I doing wrong, or how else could I achieve this?

Ignacio Alorre
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    @MartyFouts hi, thanks for shareing. Actually I tried that answer, I should have mentioned in the question that most of my code have been taken from the accepted answer, but in my case the mat is not being assigned. That is why I posted my version – Ignacio Alorre Oct 18 '21 at 05:53
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    No problem. In the future, you should mention the specific answers you have tried and why they didn't work for you. The answer from the question should work, but the code you shared is missing some of the steps. Someone has already posted another way of doing it. If you want to see your code fixed, let me know and I'll post an answer with working bmesh-based code. – Marty Fouts Oct 18 '21 at 14:52

2 Answers2

7

If you'd like to assign material(s) to certain faces in Edit Mode, just assign the index of the material slot to BMFace.material_index on a Bmesh representation of your mesh:

enter image description here

import bpy, bmesh

def create_material(mat_name, diffuse_color=(1,1,1,1)):
    mat = bpy.data.materials.new(name=mat_name)
    mat.diffuse_color = diffuse_color
    return mat


Generate 2 demo materials


mat_red = create_material("Red", (1,0,0,1))
mat_green = create_material("Green", (0,1,0,1))


Generate a Box


bpy.ops.mesh.primitive_cube_add(size=2, enter_editmode=True, location=(0, 0, 0))


Resize and Translate the box ...


Get a reference to the object in context


obj = bpy.context.object


Append both Materials to the created object


obj.data.materials.append(mat_red)
obj.data.materials.append(mat_green)


Bmesh representation


me = obj.data
bm = bmesh.from_edit_mesh(me)
bm.faces.ensure_lookup_table()


Assign the green Material to the second polygon


bm.faces[1].material_index = 1


Assign the green Material to the 4th polygon


bm.faces[3].material_index = 1


Optional


#bmesh.update_edit_mesh(me)
#bpy.ops.object.mode_set(mode='OBJECT')

You might want to create the mesh using Bmesh in this case as well: how to use BMesh to add verts, faces, and edges to existing geometry

brockmann
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6

You can assign the materials using MeshPolygon.material_index in Object Mode without Bmesh.

enter image description here

import bpy

def create_material(mat_name, diffuse_color=(1,1,1,1)):
    mat = bpy.data.materials.new(name=mat_name)
    mat.diffuse_color = diffuse_color
    return mat


Generate 2 demo materials


mat_red = create_material("Red", (1,0,0,1))
mat_green = create_material("Green", (0,1,0,1))


Generating a Box


bpy.ops.mesh.primitive_cube_add(size=2, location=(0, 0, 0))


Resizing and Translating the box ...


Get a reference to the object in context


obj = bpy.context.object


Append both Materials to the created object


obj.data.materials.append(mat_red)
obj.data.materials.append(mat_green)


Assign the green Material to the second polygon


obj.data.polygons[1].material_index = 1


Assign the green Material to the 4th polygon


obj.data.polygons[3].material_index = 1

Related:

brockmann
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