app.py

import boto3
import os

s3 = boto3.client(
    's3',
    aws_access_key_id=os.environ["AWS_ACCESS_KEY_ID"],
    aws_secret_access_key=os.environ["AWS_SECRET_ACCESS_KEY"],
    region_name='ap-northeast-1'
)

bucket_name = os.environ["BUCKET_NAME"]
key = os.environ["PYFILE_NAME"]

response = s3.get_object(Bucket=bucket_name, Key=key)
code = response['Body'].read().decode('utf-8')
exec(code)