Building Lambda functions with Python - Amazon Lambda
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Building Lambda functions with Python

You can run Python code in Amazon Lambda. Lambda provides runtimes for Python that run your code to process events. Your code runs in an environment that includes the SDK for Python (Boto3), with credentials from an Amazon Identity and Access Management (IAM) role that you manage. To learn more about the SDK versions included with the Python runtimes, see Runtime-included SDK versions.

Lambda supports the following Python runtimes.

Name Identifier Operating system Deprecation date Block function create Block function update

Python 3.12


Amazon Linux 2023

Python 3.11


Amazon Linux 2

Python 3.10


Amazon Linux 2

Python 3.9


Amazon Linux 2

Python 3.8


Amazon Linux 2

Oct 14, 2024

Feb 28, 2025

Mar 31, 2025


The runtime information in this table undergoes continuous updates. For more information on using Amazon SDKs in Lambda, see Managing Amazon SDKs in Lambda functions in Serverless Land.

To create a Python function
  1. Open the Lambda console.

  2. Choose Create function.

  3. Configure the following settings:

    • Function name: Enter a name for the function.

    • Runtime: Choose Python 3.12.

  4. Choose Create function.

  5. To configure a test event, choose Test.

  6. For Event name, enter test.

  7. Choose Save changes.

  8. To invoke the function, choose Test.

The console creates a Lambda function with a single source file named lambda_function. You can edit this file and add more files in the built-in code editor. To save your changes, choose Save. Then, to run your code, choose Test.


The Lambda console uses Amazon Cloud9 to provide an integrated development environment in the browser. You can also use Amazon Cloud9 to develop Lambda functions in your own environment. For more information, see Working with Amazon Lambda functions using the Amazon Toolkit in the Amazon Cloud9 user guide.


To get started with application development in your local environment, deploy one of the sample applications available in this guide's GitHub repository.

Sample Lambda applications in Python
  • blank-python – A Python function that shows the use of logging, environment variables, Amazon X-Ray tracing, layers, unit tests and the Amazon SDK.

Your Lambda function comes with a CloudWatch Logs log group. The function runtime sends details about each invocation to CloudWatch Logs. It relays any logs that your function outputs during invocation. If your function returns an error, Lambda formats the error and returns it to the invoker.

Runtime-included SDK versions

The version of the Amazon SDK included in the Python runtime depends on the runtime version and your Amazon Web Services Region. To find the version of the SDK included in the runtime you're using, create a Lambda function with the following code.

import boto3 import botocore def lambda_handler(event, context): print(f'boto3 version: {boto3.__version__}') print(f'botocore version: {botocore.__version__}')

Response format

In Python 3.12 and later Python runtimes, functions return Unicode characters as part of their JSON response. Earlier Python runtimes return escaped sequences for Unicode characters in responses. For example, in Python 3.11, if you return a Unicode string such as "こんにちは", it escapes the Unicode characters and returns "\u3053\u3093\u306b\u3061\u306f". The Python 3.12 runtime returns the original "こんにちは".

Using Unicode responses reduces the size of Lambda responses, making it easier to fit larger responses into the 6 MB maximum payload size for synchronous functions. In the previous example, the escaped version is 32 bytes—compared to 17 bytes with the Unicode string.

When you upgrade to Python 3.12, you might need to adjust your code to account for the new response format. If the caller expects escaped Unicode, you must either add code to the returning function to escape the Unicode manually, or adjust the caller to handle the Unicode return.

Graceful shutdown for extensions

Python 3.12 and later Python runtimes offer improved graceful shutdown capabilities for functions with external extensions. When Lambda shuts down an execution environment, it sends a SIGTERM signal to the runtime and then a SHUTDOWN event to each registered external extension. You can catch the SIGTERM signal in your Lambda function and clean up resources such as database connections that were created by the function.

To learn more about the execution environment lifecycle, see Lambda execution environment. For examples of how to use graceful shutdown with extensions, see the Amazon Samples GitHub repository.