Selected objects have the same specular and roughness value in the Principled BSDF

import bpy

for obj in bpy.context.selected_objects:
	m = obj.data.materials[0]
	m.node_tree.nodes["Principled BSDF"].inputs[1].default_value = 0.5
	m.node_tree.nodes["Principled BSDF"].inputs[2].default_value = 0.5