A gotcha I ran into while playing with AWS Lambda.

aws_lambda_gotcha.md

I started out pasting Python code into the AWS Lambda web GUI, right in that textarea. Got it working, making a call to a Slack API (whee!). So I had a working test case and I could test a refactor.

With the same code, I wanted to take advantage of the cool zipfile/ virtualenv upload support ("Create a Deployment Package") so I could use third-party libraries. Keeping the code itself the same (same as what I'd pasted into the textarea), the test should work again, as long as I packaged it right.

I kept trying to upload a zip with the same code, I thought, to AWS Lambda ... but I kept getting an error:

"module initialization error"

Or ...

module initialization error: 'NoneType' object has no attribute 'close'

I was banging my head against the wall a bit, with this.

I figured out my problem and it was just that I got screwed up with overloaded or vague terms. I was thinking at the wrong level of modularity.

In AWS I could see my configuration said to use this Handler:

lambda_function.lambda_handler

So I had a file structure like this:

└── lambda_function
    ├── __init__.py
    └── lambda_handler.py

Both are wrong. lambda_function in the default configuration for AWS Lambda refers to a module, and lamdba_handler refers to a function within the module. Seems obvious in retrospect, but the names are vague, and if you're like me ... you're not used to putting module_name.function_name in an HTML form and having stuff work.

Anyway, this is the file structure that ACTUALLY matches the default configuration:

lambda_function.py

And that's it. lambda_function.py should have:

def lambda_handler(event, context):
    # ...

So you can get that working, and then if you want, you can rename things from there.

Happy hacking :)

haha, yeah i have everything setup correctly and i still am stuck with lambda... i used github/kappa for a bit but its not usable for my case :/

@deeteecee-minion have you looked at https://www.zappa.io/ ? This is what I'll be using on my next Lambda project

Just documenting my experience, as this shows when you search for lambda module initialization error on Google:

In my case, the error was trying to access an inexistent dictionary key using my_dict["invalid_key"]. Sometimes the lack of detailed error traces in Lambda makes me crazy, but in this case I managed to find it relatively quickly.

The reason it was working locally, but not on Lambda is that the dictionary key was a variable dependent on the environment. The error was only produced in my testing Lambda env.