“ errorMessage”：“无法导入模块'lambda_function'

测试我的lambda函数后，出现以下错误消息：

{
  "errorMessage": "Unable to import module 'lambda_function'"
}

我上传了.zip仅包括以下依赖关系：requests，boto3，PIL，Pillow-4.0.0.dist-info＆lambda函数lambda_function.py-这是从AWS复制的例如：

from __future__ import print_function
import boto3
import os
import sys
import uuid
from PIL import Image
import PIL.Image

s3_client = boto3.client('s3')

def resize_image(image_path, resized_path):
    with Image.open(image_path) as image:
        image.thumbnail(tuple(x / 2 for x in image.size))
        image.save(resized_path)

def handler(event, context):
    for record in event['Records']:
        bucket = record['s3']['bucket']['name']
        key = record['s3']['object']['key'] 
        download_path = '/tmp/{}{}'.format(uuid.uuid4(), key)
        upload_path = '/tmp/resized-{}'.format(key)

        s3_client.download_file(bucket, key, download_path)
        resize_image(download_path, upload_path)
        s3_client.upload_file(upload_path, '{}resized'.format(bucket), key)

我的处理程序是： lambda_function.lambda_handler

知道是什么问题吗？