This post is written by Julian Wood, Principal Developer Advocate, and Leandro Cavalcante Damascena, Senior Solutions Architect Engineer.

AWS Lambda now supports Python 3.13 as both a managed runtime and container base image. Python is a popular language for building serverless applications. The Python 3.13 release includes a number of changes to the language, the implementation, and the standard library. With this release, Python developers can now take advantage of these new features and enhancements when creating serverless applications on Lambda. Python 3.13 also includes experimental support for a number of features, which are not available in Lambda.

You can develop Lambda functions in Python 3.13 using the AWS Management Console, AWS Command Line Interface (AWS CLI), AWS SDK for Python (Boto3), AWS Serverless Application Model (AWS SAM), AWS Cloud Development Kit (AWS CDK), and other infrastructure as code tools.

The Python 3.13 runtime allows you to implement serverless best practices using Powertools for AWS Lambda (Python). This is a developer toolkit that includes observability, batch processing, AWS Systems Manager Parameter Store integration, idempotency, feature flags, Amazon CloudWatch Metrics, structured logging, and more.

Lambda@Edge allows you to use Python 3.13 to customize low-latency content delivered through Amazon CloudFront.

Lambda runtime changes

Amazon Linux 2023

As with the Python 3.12 runtime, the Python 3.13 runtime is based on the provided.al2023 runtime, which is based on the Amazon Linux 2023 minimal container image. The Amazon Linux 2023 minimal image uses microdnf as a package manager, symlinked as dnf. This replaces the yum package manager used in Python 3.11 and earlier AL2-based images. If you deploy your Lambda functions as container images, you must update your Dockerfiles to use dnf instead of yum when upgrading to the Python 3.13 base image from Python 3.11 or earlier base images.

Learn more about the provided.al2023 runtime in the blog post Introducing the Amazon Linux 2023 runtime for AWS Lambda and the Amazon Linux 2023 launch blog post.

New Python features

Data model improvements

There are improvements to the Python data model. __static_attributes__ stores the names of attributes accessed through self.X in any function in a class body.

Typing changes

With the implementation of PEP 702, you can now use the new warnings.deprecated() decorator to mark deprecations in the type system and at runtime.

Python 3.13 also adds PEP 696, which introduces default values for type parameters. This enhancement allows developers to specify default types for TypeVar, ParamSpec, and TypeVarTuple when omitting type arguments.

Standard library

The standard library includes improvements for a new PythonFinalizationError exception, raised when an operation is blocked during finalization.

The new functions base64.z85encode() and base64.z85decode() support encoding and decoding Z85 data.

The copy module now has a copy.replace() function, with support for many built-in types and any class defining the __replace__() method.

The os module has a suite of new functions for working with Linux’s timer notification file descriptors.

There is a change to the defined mutation semantics for locals().

Experimental features that are unavailable

Python 3.13 includes a number of experimental features which are not enabled for the Lambda managed runtime or base images. These features must be enabled when the Python runtime is compiled. Since the Lambda-provided Python 3.13 runtime is intended for production workloads, these features are not enabled in the Lambda build of Python 3.13 and cannot be enabled via an execution-time flag. To use these features in Lambda, you can deploy your own Python runtime using a custom runtime or container image with these features enabled.

Free-threaded CPython

You can not enable the experimental support for running Python in a free-threaded mode, with the global interpreter lock (GIL) disabled.

Just-in-time (JIT) compiler

You can also not enable the experimental JIT compiler within the Lambda managed runtime or base image.

Performance considerations

At launch, new Lambda runtimes receive less usage than existing established runtimes. This can result in longer cold start times due to reduced cache residency within internal Lambda sub-systems. Cold start times typically improve in the weeks following launch as usage increases. As a result, AWS recommends not drawing conclusions from side-by-side performance comparisons with other Lambda runtimes until the performance has stabilized. Since performance is highly dependent on workload, customers with performance-sensitive workloads should conduct their own testing, instead of relying on generic test benchmarks.

Using Python 3.13 in Lambda

AWS Management Console

To use the Python 3.13 runtime to develop your Lambda functions, specify a runtime parameter value Python 3.13 when creating or updating a function. The Python 3.13 version is available in the Runtime dropdown in the Create Function page:

To update an existing Lambda function to Python 3.13, navigate to the function in the Lambda console and choose Edit in the Runtime settings panel. The new version of Python is available in the Runtime dropdown.

You may need to check your code and dependencies for compatibility with Python 3.13, and update as necessary.

AWS Lambda container image

Change the Python base image version by modifying the FROM statement in your Dockerfile

AWS Serverless Application Model (AWS SAM)

In AWS SAM set the Runtime attribute to python3.13 to use this version.

AWSTemplateFormatVersion: '2010-09-09' Transform: AWS::Serverless-2016-10-31 Description: Simple Lambda Function MyFunction: Type: AWS::Serverless::Function Properties: Description: My Python Lambda Function CodeUri: my_function/ Handler: lambda_function.lambda_handler Runtime: python3.13

AWS SAM supports generating this template with Python 3.13 for new serverless applications using the sam init command. Refer to the AWS SAM documentation.

AWS Cloud Development Kit (AWS CDK)

In AWS CDK, set the runtime attribute to Runtime.PYTHON_3_13 to use this version. In Python CDK:

from constructs import Construct from aws_cdk import ( App, Stack, aws_lambda as _lambda ) class SampleLambdaStack(Stack): def __init__(self, scope: Construct, id: str, **kwargs) -> None: super().__init__(scope, id, **kwargs) base_lambda = _lambda.Function(self, 'python313LambdaFunction', handler='lambda_handler.handler', runtime=_lambda.Runtime.PYTHON_3_13, code=_lambda.Code.from_asset('lambda'))

In TypeScript CDK:

import * as cdk from 'aws-cdk-lib'; import * as lambda from 'aws-cdk-lib/aws-lambda' import * as path from 'path'; import { Construct } from 'constructs'; export class SampleLambdaStack extends cdk.Stack { constructor(scope: Construct, id: string, props?: cdk.StackProps) { super(scope, id, props); // The code that defines your stack goes here // The python3.13 enabled Lambda Function const lambdaFunction = new lambda.Function(this, 'python313LambdaFunction', { runtime: lambda.Runtime.PYTHON_3_13, memorySize: 512, code: lambda.Code.fromAsset(path.join(__dirname, '/../lambda')), handler: 'lambda_handler.handler' }) } }

Conclusion

Lambda now supports Python 3.13 as a managed language runtime. This release uses the Amazon Linux 2023 OS and includes Python 3.13 language additions including data model improvements, typing changes, and updates to the standard library. This release does not support the experimental option to disable the global interpreter lock or the experimental JIT compiler.

You can build and deploy functions using Python 3.13 using the AWS Management Console, AWS CLI, AWS SDK, AWS SAM, AWS CDK, or your choice of infrastructure as code tool. You can also use the Python 3.13 container base image if you prefer to build and deploy your functions using container images.

Python 3.13 runtime support helps developers to build more efficient, powerful, and scalable serverless applications. Try the Python 3.13 runtime in Lambda today and experience the benefits of this updated language version.

For more serverless learning resources, visit Serverless Land.