How to join objects with Python?

Question

I try to do this:

bpy.ops.object.select_all()
bpy.ops.object.join()

in my script. It selects all the stuff like CtrlA but fails on join() (CtrlJ) with the following error message:

Traceback (most recent call last): File "", line 1,
in File "C:\Program Files\Blender
Foundation\Blender\2.71\scripts\modules\bpy\ops.py", line 188, in
__ call __
ret = op_call(self.idname_py(), None, kw) RuntimeError: Operator bpy.ops.object.join.poll() failed, context is incorrect

the message is from console.

How can I make this work? CtrlA, CtrlJ actually works.

Answer 1

To join an object you must have one object as the active object. If there is no active object selected it will not work. Try setting one object as the selected object.

An example would be

bpy.context.scene.objects.active = bpy.data.objects["Cube"]

Answer 2

If you don't want to change the real selection states, you may wanna use an override:

import bpy

scene = bpy.context.scene

obs = []
for ob in scene.objects:
    # whatever objects you want to join...
    if ob.type == 'MESH':
        obs.append(ob)

ctx = bpy.context.copy()

# one of the objects to join
ctx['active_object'] = obs[0]

ctx['selected_objects'] = obs
# In Blender 2.8x this needs to be the following instead:
#ctx['selected_editable_objects'] = obs

# We need the scene bases as well for joining.
# Remove this line in Blender >= 2.80!
ctx['selected_editable_bases'] = [scene.object_bases[ob.name] for ob in obs]

bpy.ops.object.join(ctx)

Answer 3

No need for bases in 2.8 join operator override.

Thought I would also post this here. It appears at 2.80 beta version, there is no need to have the selected editable bases context member, instead use selected editable objects

Testing this in python console. Have duped the default cube 3 times, the last dupe "Cube.003" is active and only object selected.

>>> C.object
bpy.data.objects['Cube.003']


>>> C.selected_objects
[bpy.data.objects['Cube.003']]

A list of all the mesh objects in scene to join

>>> obs = [o for o in C.scene.objects if o.type == 'MESH']
>>> obs
[bpy.data.objects['Cube'], bpy.data.objects['Cube.001'], bpy.data.objects['Cube.002'], bpy.data.objects['Cube.003']]

Make a context override dictionary, with only object, active_object, selected_objects, selected_editable_objects as members

>>> c = {}

>>> c["object"] = c["active_object"] = C.object
>>> c["selected_objects"] = c["selected_editable_objects"] = obs

Blender 2.8 - 3.1:

Run the operator with this override

>>> bpy.ops.object.join(c)
{'FINISHED'}

Blender 3.2+ :

with C.temp_override(active_object=C.active_object, selected_editable_objects=obs):
    bpy.ops.object.join()

Resulting scene after running. All four cubes are joined as one "Cube.003", The result desired

>>> C.scene.objects[:]
[bpy.data.objects['Lamp'], bpy.data.objects['Camera'], bpy.data.objects['Cube.003']]

Risky look at obs since three of the objects no longer exist.

>>> obs
[<bpy_struct, Object invalid>, <bpy_struct, Object invalid>, <bpy_struct, Object invalid>, bpy.data.objects['Cube.003']]

Further to this, can make object copies into the data collection and join them. Here i am copying the object 3 times, and then joining all mesh objects into file as one.

>> for i in range(3):
...     o.copy()
...  

bpy.data.objects['Cube.000']
bpy.data.objects['Cube.001']
bpy.data.objects['Cube.002']

>>> obs = [o for o in D.objects if o.type == 'MESH']

"Array them to see result"

>> for  o in obs:
...     o.location.z += ob.dimensions.z
...     
>>> c = {}
>>> c["object"] = c["active_object"] = C.object
>>> c["selected_objects"] = c["selected_editable_objects"] = obs

>>> bpy.ops.object.join(c)
{'FINISHED'}

the dupes will remain in data, the object "Cube.003" will be a mesh made of all others.

Answer 4

A full script for later reference:

import bpy

for ob in bpy.context.scene.objects:
    if ob.type == 'MESH':
        ob.select = True
        bpy.context.scene.objects.active = ob
    else:
        ob.select = False
bpy.ops.object.join()

Answer 5

here's a version of stacker's answer updated to work in 3.4.1

import bpy

for ob in bpy.context.scene.objects:
    if ob.type == 'MESH':
        ob.select_set(True)
        bpy.context.view_layer.objects.active = ob
    else:
        ob.select_set(False)
bpy.ops.object.join()