Blender Scripting

Overview

Automate Blender tasks and create 3D models procedurally using Python and the bpy API. Run scripts headlessly from the terminal to manipulate scenes, build geometry with bmesh, apply modifiers, batch process files, and import/export models.

Instructions

1. Run scripts from the terminal

blender --background --python script.py
blender myfile.blend --background --python script.py
blender --background --factory-startup --python-exit-code 1 --python script.py -- --output /tmp/result.png --scale 2.0

Your own arguments go after --; read them in the script with sys.argv[sys.argv.index("--") + 1:]. Without --python-exit-code 1, Blender exits with status 0 even when the script raised an exception, so CI and shell && chains never notice the failure. --factory-startup ignores the user's saved preferences and add-ons for reproducible runs.

2. Scene setup and cleanup

import bpy

def clear_scene():
    bpy.ops.object.select_all(action='SELECT')
    bpy.ops.object.delete(use_global=False)
    for block in bpy.data.meshes:
        if block.users == 0:
            bpy.data.meshes.remove(block)

3. Create and transform objects

import bpy, math
from mathutils import Vector

bpy.ops.mesh.primitive_cube_add(size=2, location=(0, 0, 0))
cube = bpy.context.active_object
cube.location = (3, 0, 1)
cube.rotation_euler = (0, 0, math.radians(45))
cube.scale = (1, 2, 0.5)

4. Build meshes from raw data

vertices = [(-1,-1,0), (1,-1,0), (1,1,0), (-1,1,0),
            (-1,-1,2), (1,-1,2), (1,1,2), (-1,1,2)]
faces = [(0,1,2,3), (4,5,6,7), (0,1,5,4), (2,3,7,6), (0,3,7,4), (1,2,6,5)]

mesh = bpy.data.meshes.new("CustomBox")
mesh.from_pydata(vertices, [], faces)
mesh.update()
obj = bpy.data.objects.new("CustomBox", mesh)
bpy.context.collection.objects.link(obj)

5. Use bmesh for advanced mesh editing

import bmesh

bm = bmesh.new()
v1 = bm.verts.new((0, 0, 0))
v2 = bm.verts.new((1, 0, 0))
v3 = bm.verts.new((1, 1, 0))
v4 = bm.verts.new((0, 1, 0))
bm.faces.new((v1, v2, v3, v4))

bmesh.ops.extrude_face_region(bm, geom=bm.faces[:])
bmesh.ops.subdivide_edges(bm, edges=bm.edges[:], cuts=2)

mesh = bpy.data.meshes.new("Result")
bm.to_mesh(mesh)
bm.free()
obj = bpy.data.objects.new("Result", mesh)
bpy.context.collection.objects.link(obj)

6. Apply modifiers

obj = bpy.context.active_object

sub = obj.modifiers.new("Subdivision", 'SUBSURF')
sub.levels = 2

mirror = obj.modifiers.new("Mirror", 'MIRROR')
mirror.use_axis = (True, False, False)

array = obj.modifiers.new("Array", 'ARRAY')
array.count = 5
array.relative_offset_displace = (1.1, 0, 0)

solid = obj.modifiers.new("Solidify", 'SOLIDIFY')
solid.thickness = 0.1

bevel = obj.modifiers.new("Bevel", 'BEVEL')
bevel.width = 0.05
bevel.segments = 3

# Apply permanently
bpy.context.view_layer.objects.active = obj
bpy.ops.object.modifier_apply(modifier="Subdivision")

7. Create curves

curve_data = bpy.data.curves.new("MyCurve", type='CURVE')
curve_data.dimensions = '3D'
spline = curve_data.splines.new('BEZIER')
spline.bezier_points.add(3)
for i, (x, y, z) in enumerate([(0,0,0), (1,1,0), (2,0,1), (3,1,1)]):
    pt = spline.bezier_points[i]
    pt.co = (x, y, z)
    pt.handle_left_type = pt.handle_right_type = 'AUTO'
curve_data.bevel_depth = 0.1
obj = bpy.data.objects.new("MyCurve", curve_data)
bpy.context.collection.objects.link(obj)

8. Import and export

bpy.ops.wm.obj_import(filepath="assets/chair.obj")
bpy.ops.import_scene.fbx(filepath="assets/chair.fbx")
bpy.ops.import_scene.gltf(filepath="assets/chair.glb")
bpy.ops.wm.obj_export(filepath="build/chair_out.obj")
bpy.ops.export_scene.gltf(filepath="build/chair_out.glb", export_format='GLB')
bpy.ops.wm.stl_export(filepath="build/chair_out.stl")

The OBJ operators are wm.obj_import / wm.obj_export; the old import_scene.obj / export_scene.obj were removed in 4.0. FBX and glTF stay under import_scene / export_scene.

9. Assign materials

mat_red = bpy.data.materials.new("Red")
bsdf = next(n for n in mat_red.node_tree.nodes if n.type == "BSDF_PRINCIPLED")
bsdf.inputs["Base Color"].default_value = (0.8, 0.05, 0.05, 1)
bsdf.inputs["Roughness"].default_value = 0.4
mat_red.diffuse_color = (0.8, 0.05, 0.05, 1)   # viewport colour only

mat_grey = bpy.data.materials.new("Grey")
obj.data.materials.append(mat_red)    # slot 0
obj.data.materials.append(mat_grey)   # slot 1
for i, poly in enumerate(obj.data.polygons):
    poly.material_index = 0 if i % 2 == 0 else 1

In Blender 5.0+ a new material already has a node tree with a Principled BSDF, and the use_nodes flag is deprecated (it warns and is due for removal in 6.0). On 4.x and older, set mat_red.use_nodes = True first. Find the node by type, not by its name, which is translated in non-English interfaces. diffuse_color affects only the viewport, not renders. A material_index needs a matching slot, so append both materials first.

10. Batch process files

import glob
for filepath in glob.glob("scenes/*.blend"):
    bpy.ops.wm.open_mainfile(filepath=filepath)
    for obj in bpy.data.objects:
        if obj.type == 'MESH':
            print(f"  {obj.name}: {len(obj.data.vertices)} verts")
    bpy.ops.wm.save_as_mainfile(filepath=filepath.replace(".blend", "_processed.blend"))

Examples

Example 1: Procedural spiral staircase

User request: "Generate a spiral staircase with 20 steps"

import bpy, math

def create_spiral_staircase(steps=20, radius=3, height=6):
    bpy.ops.object.select_all(action='SELECT')
    bpy.ops.object.delete()
    step_height = height / steps
    for i in range(steps):
        angle = (2 * math.pi * i) / steps
        x, y = radius * math.cos(angle), radius * math.sin(angle)
        bpy.ops.mesh.primitive_cube_add(size=1, location=(x, y, i * step_height),
                                         scale=(1.5, 0.4, step_height * 0.8))
        bpy.context.active_object.rotation_euler.z = angle
    bpy.ops.mesh.primitive_cylinder_add(radius=0.2, depth=height, location=(0, 0, height/2))

create_spiral_staircase()
bpy.ops.wm.save_as_mainfile(filepath="/tmp/staircase.blend")

Example 2: Export all mesh objects as separate OBJ files

User request: "Export every mesh in my .blend as a separate OBJ"

import bpy, os
output_dir = "/tmp/exports"
os.makedirs(output_dir, exist_ok=True)
for obj in bpy.data.objects:
    if obj.type == 'MESH':
        bpy.ops.object.select_all(action='DESELECT')
        obj.select_set(True)
        bpy.context.view_layer.objects.active = obj
        bpy.ops.wm.obj_export(filepath=os.path.join(output_dir, f"{obj.name}.obj"),
                               export_selected_objects=True)

Run: blender scene.blend --background --python export_all.py

Example 3: Procedural terrain from heightmap

User request: "Generate a terrain mesh using sine waves"

import bpy, bmesh, math, random
bm = bmesh.new()
res, size = 50, 20
verts = []
for i in range(res):
    row = []
    for j in range(res):
        x, y = (i/res - 0.5) * size, (j/res - 0.5) * size
        z = math.sin(x*0.5) * math.cos(y*0.5) * 2 + random.uniform(-0.2, 0.2)
        row.append(bm.verts.new((x, y, z)))
    verts.append(row)
for i in range(res-1):
    for j in range(res-1):
        bm.faces.new((verts[i][j], verts[i+1][j], verts[i+1][j+1], verts[i][j+1]))
mesh = bpy.data.meshes.new("Terrain")
bm.to_mesh(mesh)
bm.free()
obj = bpy.data.objects.new("Terrain", mesh)
bpy.context.collection.objects.link(obj)

Guidelines

• Always use --background when running from the terminal to skip the GUI
• Use from_pydata() for simple static meshes; use bmesh for advanced operations
• Always call mesh.update() after from_pydata() and bm.free() after bmesh
• Use bpy.data for direct data access (fast); use bpy.ops for complex operations
• Ensure correct object is active and selected before using operators
• For batch processing, save to new files (not overwrite originals) unless requested
• For large meshes (10k+ faces), prefer bmesh over repeated bpy.ops calls
• Link objects to a collection — unlinked objects won't appear in the scene
• Blender uses Z-up coordinates; account for this when importing from Y-up systems
• Use mathutils for vector math and matrix operations (bundled with Blender Python)
• Import/export operator names vary by Blender version; the ones listed here were run on 5.0.1 and match the 3.6+ names