A Quick Way to Test Python Lambda Functions Locally


2 min read

I'm working on a more expansive post on Lambda functions and API Gateway, but I wanted to share a find that I think is useful when testing Lambda functions written in Python.

The pip package python-lambda-local will help you emulate calling a Lambda function, without having to leave your local machine.

To install and setup, create a simple py file, add a handler function that takes an event, then call the handler, filename and a sample json payload from file.

Here's a simple example:

Install the package. Might be best to use venv, or you can install globally to call it from anywhere on your machine.

pip install python-lambda-local


def handler(event, context):
    msg = "Greetings %s from %s!" % (event["name"], event["city"])
    return { 
        'statusCode': 200,
        'isBase64Encoded': False,
        'body': {
            'msg': msg
        'headers': {
            'Content-Type': 'application/json'

Create an event file with some json in it event.json

    "name": "Joe",
    "city": "Ohio"

Run this command to test.

python-lambda-local -f handler app.py event.json

Check for success or error:

{'statusCode': 200, 'isBase64Encoded': False, 'body': {'msg': 'Greetings Joe from Ohio. !'}, 'headers': {'Content-Type': 'application/json'}}

That's all for today. Short and sweet, but it's all part of a larger post that I didn't have time to finish today.