Assign new material slot and random colors to existing objects

Question

I am trying since days to assign new materials and random colors to meshes that already exist in a Blender scene. I need to do it in Python but I cannot find a solution. I would like each mesh to have different materials and different colors. I have found two scripts that are very useful but I don't manage to combine them together, can anyone help please? Thank you in advance

Script 1) assign a new material to all the meshes in a scene (but color not assigned):

import bpy

bpy.ops.object.select_all(action='SELECT')

# I separated the creation of nodes to a function so it's easier 
# to edit later if needed
def create_nodes(mat): 
    mat.use_nodes = True
    nodes = mat.node_tree.nodes
    for every_node in nodes: # this removes all existing nodes
        nodes.remove(every_node)

    # creating Principled node and moving it:
    node = nodes.new('ShaderNodeBsdfPrincipled')
    node.location = (-190,100)

    # creating Output node and moving it:
    output_node = nodes.new('ShaderNodeOutputMaterial')
    output_node.location = (40,100)

    # creating the link between the two nodes:
    links = mat.node_tree.links
    link = links.new(node.outputs[0], output_node.inputs[0])

# this saves the currently active object so it can be restored later
active = bpy.context.object 

# let's loop through all selected objects
for every_object in bpy.context.selected_objects: 
    # I only want to work with objects capable of having a material
    if every_object.type in {'MESH','CURVE', 'SURFACE','META', 'FONT'}: 
        if every_object.name not in bpy.data.materials:
        # if there is no material named after the object yet let's make one
            mat = bpy.data.materials.new(every_object.name)
            # and let's create the nodes for it
            create_nodes(mat)
        else:
            # if the material already exists let's just use it
            mat = bpy.data.materials.get(every_object.name)
        if len(every_object.material_slots) == 0: # if there are no material slots
            every_object.data.materials.append(mat)

        # The only thing left now is to assign the material to 
        # all material slots. We probably do not want to loose the info
        # about how the object is divided into separate materials
        for every_slot in every_object.material_slots:
            every_slot.material = mat 

Script 2) assign a new material and a random color to an existing object in the scene (but works only for 1 object):

import bpy, random

ob = bpy.data.objects.get("Cube")
if ob != None:
    # Create materials.
    mat_one = bpy.data.materials.get("mat_one")
    if mat_one == None:
        mat_one = bpy.data.materials.new("mat_one")
    mat_one.diffuse_color = (random.random(),random.random(),random.random(),random.random())
    
     # Add materials to slots.       
    if len(ob.material_slots) != 1:     
        ob.data.materials.append(mat_one)