Purge unused data (e.g. particle system, or groups) by script

Question

How can I completely remove a objects (e.g. particle system or groups used in particle systems) in blender using python?

The problem is this: I have a script, with which I create a scene (e.g. adding some normal objects and some group of objects with a particle system). For a research study I would like to repeat that that several times, without restarting blender. So I can create a scene, delete everything, e.g. with a script like this:

import bpy
scn = bpy.context.scene
for obj in scn.objects:
    obj.select = True
bpy.ops.object.delete()

If I rerun the script to recreate the scene with objects using particle system, the latter is not shown in the scene anymore (only the placeholders of the particle system). Now I'm not sure where exactly the problem lies, but I guess not everything is immediately deleted, running the script above. Only the startup of blender helps (but that's not what I want) or pushing the purge button. The purge button seems to start the command:

bpy.ops.outliner.orphans_purge()

But I can't get this piece of code to run in the console. It says that "the context is incorrect". Is there a way to purge the unused data by python script? Thanks a lot for any help.

Answer 1

To permanently delete curve data blocks that have no users without reloading the project file (which can be bit problematic at times), you can use this python code:

import bpy
from bpy import data as D

for block in D.curves:
    if block.users == 0:
        D.curves.remove(block)

It'll iterate through all data blocks of type "Curve" and delete them if they have no users.

Answer 2

You can remove all unlinked data blocks with the following solution. This way you can make sure there will never be any memory leakage what so ever and you will not need to save a .blend file and reopen it.

First remove the meshes/objects with the following code:

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

where you can check type against any of the following values according to [this documentation][1]:

[‘MESH’, ‘CURVE’, ‘SURFACE’, ‘META’, ‘FONT’, ‘ARMATURE’, ‘LATTICE’, ‘EMPTY’, ‘CAMERA’, ‘LAMP’, ‘SPEAKER’]

Then you can execute the following code snippet to remove all the unused blocks. This way you don't have to close/open Blender or save/open a .blend file:

for block in bpy.data.meshes:
    if block.users == 0:
        bpy.data.meshes.remove(block)

for block in bpy.data.materials:
    if block.users == 0:
        bpy.data.materials.remove(block)

for block in bpy.data.textures:
    if block.users == 0:
        bpy.data.textures.remove(block)

for block in bpy.data.images:
    if block.users == 0:
        bpy.data.images.remove(block)

IMPORTANT NOTE: It looks like that there is some dependencies between some data blocks such as mesh, texture, image and materials. If you do not remove the data blocks on the highest level of the hierarchy, you will not be able to remove other data blocks or you have to take the risk and remove data blocks with users more than 0. So make sure you use the code above in the following order to remove data blocks. This way you can remove all unlinked (users == 0) data blocks:

remove meshes --> remove materials --> remove textures --> remove images

The followings also have data blocks:

bpy.data.curves
bpy.data.lamps
bpy.data.cameras

Answer 3

The following python script solved the problem in that case (all the orphaned data was removed). After that, the objects with particle system can be rebuilt and the particle system is displayed properly.

import bpy
scn = bpy.context.scene  
for obj in scn.objects:
    obj.select = True
bpy.ops.object.delete()

bpy.ops.wm.save_mainfile(filepath="/...../test.blend")
bpy.ops.wm.open_mainfile(filepath="/...../test.blend")