AWS Developer Tools Blog

Chalice 0.4 & 0.5 Deliver Local Testing and Multifile Application Capabilities for Python Serverless Application Development

We’re continuing to add features to Chalice, a preview release of our microframework for Python serverless application development using AWS Lambda and Amazon API Gateway. Chalice is designed to make it simple and fast for Python developers to create REST APIs built in a serverless framework.

In our latest releases, we’ve added initial versions for a couple of the most commonly requested features:

  1. Save time by testing APIs locally before deploying to Amazon API Gateway. In this first version of local testing support for Chalice, we’ve delivered a local HTTP server you can use to test and debug a local version of your python app. This enables you to avoid the work of deploying to API Gateway before you validate APIs.
  2. Build more complex applications with more complex initial support for multifile python apps. Chalice 0.4 enables Python developers to maintain their preferred best practices and coding styles for applications that would not normally be contained within one single file, and to include files of other types as part of the deployment package. This improves on our earlier Chalice releases where deployment packages were limited to the file.

We’ve also improved existing capabilities that make it easier to build and manage your serverless apps.

  1. More configurable logging with improved readability. We’ve added the ability to configure logging for the app object, where previously logging was configured on the root logger. This update enables you to configure logging levels and log format, and eliminates some duplicate log entries seen in previous versions of Chalice.
  2. Improved ability to retrieve your app’s Amazon API Gateway URL. We’ve included a chalice url command which enables you to programmatically retrieve the URL of your API; in previous versions this was a manual process.

Our releases continue to be focused on feedback and requests from the developer community. Want to learn more? Here are a few suggestions.

Try building a serverless application with Chalice. Chalice is available on PyPI (pip install chalice) and GitHub ( – check out the README for tutorials). It’s published as a preview project and is not yet recommended for production APIs. You can also see our original Chalice blog post where we introduced a preview release of Chalice.

Stay tuned for new capabilities to be released. You can check out the working list of features for our upcoming release here:

Let us know what you think. We look forward to your feedback and suggestions. Feel free to leave comments here or come talk to us on GitHub.
Planning to attend AWS re:Invent? Come check out our re:Invent session focused on Chalice where we will present new features and go through demos, such as how to deploy a REST API in less than 30 seconds. You can add this session to your re:Invent schedule here, or sign up for the re:Invent live stream.