Why does view_layer.update seemingly fail for my armature?

Question

I'm writing an export script for an armature (using Blender 3.0.0). In this script, I'm attempting to clear bone roll, then force local bone matrices (bone.matrix_local) to be recomputed before writing to a file, as follows:

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

# I could also use bpy.ops.armature.roll_clear()
for editBone in armature.edit_bones:
    editBone.roll = 0

# I've tried this script with and without the following line (setting the armature's node to be active).
bpy.context.view_layer.objects.active = node
bpy.context.view_layer.update()

This seemingly has no effect, as I've confirmed that exported local bone matrices include roll (rather than zeroing roll first). What am I missing? How can I force the export script to recompute bone matrices immediately?

Answer 1

Generally you need to exit edit mode for changes to be applied. It works the same way for meshes actually. For example

# Make sure the armature is the thing you're editing
bpy.context.view_layer.objects.active = arma_ob

# Switch to edit mode
if bpy.context.mode != 'EDIT':
    bpy.ops.object.mode_set(mode='EDIT')

# Clear all rolls
for editBone in arma_ob.data.edit_bones:
    editBone.roll = 0

# Exit edit mode
bpy.ops.object.mode_set(mode='OBJECT')

# Access the new bone.matrix_local here