uvunwrap a blender object using a script

uvproject.py

# save this as uvproject.py and use the following command
# blender -b test.blend -P uvproject.py

import bpy

# Deselect all
bpy.ops.object.select_all(action='DESELECT')

for obj in bpy.context.scene.objects:
    if obj.type == 'MESH':
        obj.select_set(state=True)
        bpy.context.view_layer.objects.active = obj
        bpy.ops.object.mode_set(mode='EDIT')
        bpy.ops.mesh.select_all(action='SELECT')
        if len(obj.data.uv_layers) == 0:
            obj.data.uv_layers.new()
        bpy.ops.uv.smart_project()
        bpy.ops.object.mode_set(mode='OBJECT')
        bpy.ops.wm.save_mainfile()