append.py

import bpy
import os

def append_group(filepath, name, link=False, relative=False):
    return append_element(filepath, "groups", name, link, relative)

def append_collection(filepath, name, link=False, relative=False):
    return append_element(filepath, "collections", name, link, relative)

def append_object(filepath, name, link=False, relative=False):
    return append_element(filepath, "objects", name, link, relative)

def append_material(filepath, name, link=False, relative=False):
    return append_element(filepath, "materials", name, link, relative)

def append_scene(filepath, name, link=False, relative=False):
    return append_element(filepath, "scenes", name, link, relative)

def append_world(filepath, name, link=False, relative=False):
    return append_element(filepath, "worlds", name, link, relative)

def append_nodetree(filepath, name, link=False, relative=False):
    return append_element(filepath, "node_groups", name, link, relative)

def append_element(filepath, collection, name, link, relative):
    if os.path.exists(filepath):

        with bpy.data.libraries.load(filepath, link=link, relative=relative) as (data_from, data_to):
            if name in getattr(data_from, collection):
                getattr(data_to, collection).append(name)

            else:
                print("%s does not exist in %s/%s" % (name, filepath, collection))
                return

        return getattr(data_to, collection)[0]

    else:
        print("The file %s does not exist" % (filepath))