Guides

Your First AWS Lambda Function in Python (Step by Step in the Console)

By Ravindra Bagale, AWS & DevOps trainer · LinkedIn · Published: 29 September 2026 · Last updated: 30 September 2026

To create your first AWS Lambda function in Python, open Lambda → Create function → Author from scratch, enter a name, choose the latest Python 3.x runtime and Create a new role with basic Lambda permissions, then click Create function. Edit lambda_handler(event, context) in lambda_function.py, click Deploy, create a test event and click Test. The response and the print() output appear on the screen, and the full logs go to CloudWatch Logs under /aws/lambda/<function-name>.

import json

def lambda_handler(event, context):
    name = event.get("name", "mitra")
    print(f"Request for {name}")          # goes to CloudWatch Logs
    return {
        "statusCode": 200,
        "body": json.dumps({"message": f"Namaskar {name}! Hello from Lambda"})
    }

What do I need before creating a Lambda function?

• An AWS account and an IAM user (not root) — see How to Create an IAM User with MFA.
• Nothing to install. Everything happens in the browser. (Later you can deploy from your laptop with the AWS CLI.)
• 15 minutes. Lambda has a monthly free allowance of requests and compute time; check the AWS Lambda pricing page for the current numbers.

What happens when a Lambda function is triggered?

Event = the input (a JSON document from a test, an HTTP call, an S3 upload, a schedule). Handler = the Python function Lambda calls with that event. Execution role = the IAM role that decides what your code may do in AWS; the basic role only allows writing logs.

How do I create my first Lambda function in Python?

Step 1 — Create the function

Choose your region (for example Asia Pacific (Mumbai)) → Lambda → Create function → Author from scratch:

Click Create function.

Step 2 — Write the code

The editor opens lambda_function.py with a sample. Replace it with the code from the quick answer above. Lambda calls the function named in Runtime settings → Handler: lambda_function.lambda_handler means file lambda_function.py, function lambda_handler.

Step 3 — Deploy

Click Deploy. Until you deploy, Lambda keeps running the old code. The editor shows that there are undeployed changes.

Step 4 — Create a test event and run it

Click Test → Create new test event → event name ravi-test → Event JSON:

{ "name": "Ravi" }

Save, then Test again. The result shows:

{
  "statusCode": 200,
  "body": "{\"message\": \"Namaskar Ravi! Hello from Lambda\"}"
}

Below it you see the Function Logs (with your print() line), the duration and the memory used. Your first serverless code just ran. ⚡

Step 5 — Read the logs in CloudWatch

Monitor tab → View CloudWatch logs → log group /aws/lambda/hello-ravindra → newest log stream. Every invocation writes a START, your print() output, an END and a REPORT line with the billed duration.

Step 6 — Optional: call the function from a browser

Configuration → Function URL → Create function URL → auth type NONE (for this short demo only) → Save. The console adds the permission the URL needs. When called through the URL, the query string arrives in event["queryStringParameters"], so update the first line of the handler and Deploy:

    name = (event.get("queryStringParameters") or {}).get("name") or event.get("name", "mitra")

Open https://<url-id>.lambda-url.ap-south-1.on.aws/?name=Ravi — the JSON message appears in the browser. A URL with auth NONE is public, so delete it after the demo (Function URL → Delete), or use AWS_IAM auth.

Step 7 — Settings worth knowing

To give the function access to, for example, one S3 bucket, add only that permission to its execution role — least privilege, the same idea as an IAM role on EC2. To remove everything: Actions → Delete function, then delete the log group in CloudWatch if you like.

How do I fix common Lambda errors?

Ghabru naka 😅 — these are the usual ones: