Demand Python script keep running until timeline animation stop

Question

I have a script to run animation which is simulating sewing clothes. Below is a part of my code to add handle and start animation.

def sew(body_name, garment_name, export_body):
    body_obj = bpy.data.objects[body_name]
    garment_obj = bpy.data.objects[garment_name]
    s = bpy.context.scene
    s.frame_start = 1
    s.frame_end = 40
    s.frame_current = 1
    def stop_playback(scene):
        if scene.frame_current == 25:
            bpy.ops.screen.animation_cancel(restore_frame=False)
            after_sew(garment_name, export_body)
    bpy.app.handlers.frame_change_post.append(stop_playback)
    bpy.ops.screen.animation_play()

While intending to run the sewing animation from frame 1 to frame 25, I want to keep the python execution active so it will run after_sew() when the animation is done. When I run the script inside Blender's TextEditor, it does wait until the animation complete, and the after_sew() function does run accordingly. However, when I try to run this in background:

    blender myblend.blend -b --python sewing.py

The script will compile until this sew() function, start the animation, but then exit immediately without waiting for the animation reach frame 25, thus after_sew() will not run.

Is there any way to make python wait until animation done with an UI-less Blender?

I've found other similar thread talking about animation, but they are mostly about rendering with a camera which I don't need. What I only need is to export the sewed cloth at frame 25 using the after_sew() function.

Why does the animation need to play. Does script not work if you iteratively set the scene frame? — batFINGER, Oct 01 '21 at 09:08
How can I do that? Didn't know there is a way to iteratively set the scene frame. And will that work in a UI-less Blender? — kelvin hong 方, Oct 01 '21 at 15:20
No problem @kelvinhong方 Recently updated: What is the Python script to set the current frame Does that answer your question? — brockmann, Oct 02 '21 at 06:52

score 0 · Accepted Answer · answered Oct 03 '21 at 11:28

It turns out that I don't need handler. Just iteratively change the frames as suggested by @batFINGER and @brockmann

def sew(body_name, garment_name, export_body):
    body_obj = bpy.data.objects[body_name]
    garment_obj = bpy.data.objects[garment_name]
    s = bpy.context.scene
    s.frame_start = 1
    s.frame_end = 40
    s.frame_current = 1
    for i in range(2, 26):
        bpy.context.scene.frame_set(i)

And this does work with a headless Blender.

Demand Python script keep running until timeline animation stop

1 Answers1