Lambda + Python + Exit Code

Question

I've encountered an issue with a simple AWS Lambda function written in Python.

When I run my Lambda function, my code is running as expected, the result is correct, but still ends with an error code (exit code): "Process exited before completing request", this is causing the Lambda to run 3 times (async).

Do you have any best practice to manage the exit code for Lambda ?

#!/usr/bin/python

import boto3
import sys
import tweepy
import datetime

session = boto3

# Init s3 client
s3 = session.resource('s3')

def get_data_and_push(s3_bucket, s3_key, user):
    # Retrieve CSV file
    try:
        dest = s3.Object(s3_bucket, s3_key)
        dest.download_file(tmpfile)
    except Exception, e:
        print 'An error occured while trying to download CSV file'
        print 'This exception has been thrown :'
        print e
        sys.exit(1)

    # Authenticate to Twitter
    try:
        auth = tweepy.OAuthHandler(t_consumer_key, t_consumer_secret)
        auth.set_access_token(t_access_token_key, t_access_token_secret)
        api = tweepy.API(auth)
    except Exception, e:
        print 'Cannot authenticate to Twitter.'
        print 'This exception has been thrown :'
        print e
        sys.exit(2)

    data = api.get_user(user)
    print 'User : ' + data.screen_name
    print 'Followers : ' + str(data.followers_count)
    print 'Friends : ' + str(data.friends_count)
    print '-----------'

    # Get today's date
    today = datetime.datetime.now().strftime("%Y-%m-%d")

    # Write result
    try:
        # Write result at the end of the file
        file = open(tmpfile, 'a')
        file.write(today + ',' + str(data.followers_count) + ',' + str(data.friends_count)+ '\n')
        file.close()
    except Exception, e:
        print 'Unable to write in temp file'
        print 'This exception has been thrown :'
        print e
        sys.exit(5)

    # Upload final file
    try:
        # Push file to S3
        dest.upload_file(tmpfile)
    except Exception, e:
        print 'An error occured while trying to upload CSV file'
        print 'This exception has been thrown :'
        print e
        sys.exit(6)

def main(event, context):
    for user in userlist:
        get_data_and_push(bucket, 'export_' + user + '.csv', user)
    sys.exit(0)

Thanks for your help,

Answer 1

Short

Yes, remove the sys.exit(0) at the end of your code, that should do it :-)

---

Longer

By doing sys.exit(0) you actually stop the process running your code in the Lambda Function. And this is not expected by the executor.

I assume the handler of a Lambda Function is actually run from within AWS's framework. Hence you already are in a python process, and your handler is called somewhere in AWS's code. So if you exit the process, you actually short-cut AWS's framework, which cannot handle the resolution of the Lambda's execution.