This template references an image that was [pre-built](https://containers.dev/implementors/reference/#prebuilding) to automatically include needed devcontainer.json metadata.

* **Image**: mcr.microsoft.com/devcontainers/python ([source](https://github.com/devcontainers/images/tree/main/src/python))
* **Applies devcontainer.json contents from image**: Yes ([source](https://github.com/devcontainers/images/blob/main/src/python/.devcontainer/devcontainer.json))

## Using this template

This template creates two containers, one for Python and one for PostgreSQL. You will be connected to the Python container, and from within that container the PostgreSQL container will be available on **`localhost`** port 5432. The default database is named `postgres` with a user of `postgres` whose password is `postgres`, and if desired this may be changed in `.devcontainer/docker-compose.yml`. Data is stored in a volume named `postgres-data`.

While the template itself works unmodified, it uses the `mcr.microsoft.com/devcontainers/python` image which includes `git`, a non-root `vscode` user with `sudo` access, and a set of common dependencies and Go tools for development.

You also can connect to PostgreSQL from an external tool when connected to the Dev Contaner from a local tool by updating `.devcontainer/devcontainer.json` as follows:

```json
"forwardPorts": [ "5432" ]
```

Once the PostgreSQL container has port forwarding enabled, it will be accessible from the Host machine at `localhost:5432`. The [PostgreSQL Documentation](https://www.postgresql.org/docs/14/index.html) has:

1. [An Installation Guide for PSQL](https://www.postgresql.org/docs/14/installation.html) a CLI tool to work with a PostgreSQL database.
2. [Tips on populating data](https://www.postgresql.org/docs/14/populate.html) in the database. 

### Adding another service

You can add other services to your `docker-compose.yml` file [as described in Docker's documentation](https://docs.docker.com/compose/compose-file/#service-configuration-reference). However, if you want anything running in this service to be available in the container on localhost, or want to forward the service locally, be sure to add this line to the service config:

```yaml
# Runs the service on the same network as the database container, allows "forwardPorts" in devcontainer.json function.
network_mode: service:db
```

### Installing or updating Python utilities

This container installs all Python development utilities using [pipx](https://pipxproject.github.io/pipx/) to avoid impacting the global Python environment. You can use this same utility add additional utilities in an isolated environment. For example:

```bash
pipx install prospector
```

See the [pipx documentation](https://pipxproject.github.io/pipx/docs/) for additional information.

### Using the forwardPorts property

By default, web frameworks and tools often only listen to localhost inside the container. As a result, we recommend using the `forwardPorts` property to make these ports available locally.

```json
"forwardPorts": [9000]
```

The `ports` property in `docker-compose.yml` [publishes](https://docs.docker.com/config/containers/container-networking/#published-ports) rather than forwards the port. This will not work in a cloud environment like Codespaces and applications need to listen to `*` or `0.0.0.0` for the application to be accessible externally. Fortunately the `forwardPorts` property does not have this limitation.