Create a hello world Mattermost App in Python

This quick start guide will walk you through the basics of creating a hello world Mattermost App in Python. In this guide you will review an App that:

• Contains a manifest.json, declares itself an HTTP application that uses a bot account and attaches to locations in the user interface.
• Contains a form with a submit function that can launch a modal (if applicable) and send an interpolated message back to the user.
• Attaches an icon button to the channel header and creates /first-command and /second-command slash commands to provide functionality.

Prerequisites 

Before you can start with your App, you should first set up your environment by following the developer setup guide.

You also need Python version 3 installed.

Download and start the App 

In the same mattermost-app-examples repository you cloned via the developer setup guide above, navigate to the `python/hello-world` directory and start the Docker container:

cd python/hello-world
docker compose up

You’ll see Docker install the Python modules and then the App will come online and print the following message:

Running on http://mattermost-apps-python-hello-world:8090

Install the App on Mattermost 

Next, access your development Mattermost Server at http://localhost:8065 and use the /apps install http http://mattermost-apps-python-hello-world:8090/manifest.json slash command to install the hello world App. Select Agree to grant the app access to APIs and Locations and click Submit to finish the installation.

Use the App 

Select the “Hello World” channel header button in Mattermost, which brings up a modal:

Type testing and select Submit, you should see:

You can use /second-command send testing to achieve the same result.

You can also use the /first-command to see a standalone command:

Review the App 

To understand the App, examine the following elements:

Manifest 

The App has to provide a manifest, which declares the App’s metadata required for installation. In this example, the following permissions and locations are requested:

• Create posts as a bot (act_as_bot)
• Render icons in the channel header (/channel_header)
• Create slash commands (/command)

Bindings and locations 

Bindings specify how an App’s calls should be displayed and invoked from these locations. This App adds a channel header button and slash commands. In order to register these locations, there is a POST handler for the /bindings endpoint in your App’s API.

Call handlers and forms 

Call handlers are functions that respond to user interactions and webhook events. Forms handle user events on the bindings. This App provides a form before POSTing to the /submit function. In the case of a channel header, the form will launch a modal to collect its fields. In the case of a slash command, the form’s fields will be collected as arguments from the user’s command.

Assets 

Apps may include static assets (e.g., icon.png). Static assets must be served under the static path. For example, there is a icon.png file in the src/static directory that this App serves.

Uninstall the App 

Once you’re done with the App, you can uninstall it via the /apps uninstall hello-world slash command. Alternatively, you can use /apps debug clean to remove all data for all installed Apps.

To stop and clean up the App from Docker after you’re done, use the following command in the python/hello-world directory:

docker compose down

Conclusion 

You now know how to create a Mattermost App in Python. If you have questions about building Apps or want to show off what you’re building, join us on the Mattermost Apps channel in the Mattermost Community server!