Testing lambda Layers in Python

custom_func.py

def cust_fun():
    print("Hello from the deep layers!!:")
    return 1

lambda_function.py

import json
import sys
import os

sys.path.append('/opt/python_libs')

import custom_func as cf

def lambda_handler(event, context):
    print os.listdir("/opt/python_libs/.")
    cf.cust_fun()
    return {
        'statusCode': 200,
        'body': json.dumps('Hello from Lambda Layers!')
    }