Custom module import example using AWS Lambda Layers (Python)

custom_import.py

"""
  When a custom lambda layer (zipped folder) is added, all lambda functions that use it put it on "/opt/LAYER".
  In theory, "/opt/LAYER" should be added to the $PATH environment variable, but that didn't happen.
  In any case, this is an example of how to import in an "absolute" fashion.
  sample_lib/layer_test.py (That's the structure of the layer, which has a class named X.)
"""

import json
import os
import importlib.util
spec = importlib.util.spec_from_file_location("sample_lib.layer_test", "/opt/sample_lib/layer_test.py")
foo = importlib.util.module_from_spec(spec)
spec.loader.exec_module(foo)

def fetch(event, context):
    directories = os.popen("find /opt/* -type d -maxdepth 4").read().split("\n")
    body = {
        'directories': directories,
        'imported': foo.X()()
    }

    response = {
        "statusCode": 200,
        "headers": {
            "Access-Control-Allow-Origin": "*"
        },
        "body": json.dumps(body)
    }

    return response

# X

class X:
  def __call__(self):
    return("Yay, layers work!")

"""
  The invoke response is:
  {"statusCode": 200, "headers": {"Access-Control-Allow-Origin": "*"}, "body": "{\"directories\": [\"/opt/sample_lib\", \"\"], \"imported\": \"Yay, layers work!\"}"}
"""