---
title: Use containers for Python development
linkTitle: Develop your app
weight: 40
keywords: python, local, development
description: Learn how to develop your Python application locally.
aliases:
  - /language/python/develop/
  - /guides/language/python/develop/
---

## Prerequisites

Complete [Containerize a Python application](containerize.md).

## Overview

In this section, you'll learn how to set up a development environment for your containerized application. This includes:

- Adding a local database and persisting data
- Configuring Compose to automatically update your running Compose services as you edit and save your code

## Get the sample application

You'll need to clone a new repository to get a sample application that includes logic to connect to the database.

1. Change to a directory where you want to clone the repository and run the following command.

   ```console
   $ git clone https://github.com/estebanx64/python-docker-dev-example
   ```

2. In the cloned repository's directory, manually create the Docker assets or run `docker init` to create the necessary Docker assets.

   {{< tabs >}}
   {{< tab name="Use Docker Init" >}}

   In the cloned repository's directory, run `docker init`. Refer to the
   following example to answer the prompts from `docker init`.

   ```console
   $ docker init
   Welcome to the Docker Init CLI!

   This utility will walk you through creating the following files with sensible defaults for your project:
     - .dockerignore
     - Dockerfile
     - compose.yaml
     - README.Docker.md

   Let's get started!

   ? What application platform does your project use? Python
   ? What version of Python do you want to use? 3.11.4
   ? What port do you want your app to listen on? 8001
   ? What is the command to run your app? python3 -m uvicorn app:app --host=0.0.0.0 --port=8001
   ```

   Create a file named `.gitignore` with the following contents.

   ```text {collapse=true,title=".gitignore"}
   # Byte-compiled / optimized / DLL files
   __pycache__/
   *.py[cod]
   *$py.class

   # C extensions
   *.so

   # Distribution / packaging
   .Python
   build/
   develop-eggs/
   dist/
   downloads/
   eggs/
   .eggs/
   lib/
   lib64/
   parts/
   sdist/
   var/
   wheels/
   share/python-wheels/
   *.egg-info/
   .installed.cfg
   *.egg
   MANIFEST

   # Unit test / coverage reports
   htmlcov/
   .tox/
   .nox/
   .coverage
   .coverage.*
   .cache
   nosetests.xml
   coverage.xml
   *.cover
   *.py,cover
   .hypothesis/
   .pytest_cache/
   cover/

   # PEP 582; used by e.g. github.com/David-OConnor/pyflow and github.com/pdm-project/pdm
   __pypackages__/

   # Environments
   .env
   .venv
   env/
   venv/
   ENV/
   env.bak/
   venv.bak/
   ```

   {{< /tab >}}
   {{< tab name="Manually create assets" >}}

   If you don't have Docker Desktop installed or prefer creating the assets
   manually, you can create the following files in your project directory.

   Create a file named `Dockerfile` with the following contents.

   ```dockerfile {collapse=true,title=Dockerfile}
   # syntax=docker/dockerfile:1

   # Comments are provided throughout this file to help you get started.
   # If you need more help, visit the Dockerfile reference guide at
   # https://docs.docker.com/go/dockerfile-reference/

   # Want to help us make this template better? Share your feedback here: https://   forms.gle/ybq9Krt8jtBL3iCk7

   ARG PYTHON_VERSION=3.11.4
   FROM python:${PYTHON_VERSION}-slim as base

   # Prevents Python from writing pyc files.
   ENV PYTHONDONTWRITEBYTECODE=1

   # Keeps Python from buffering stdout and stderr to avoid situations where
   # the application crashes without emitting any logs due to buffering.
   ENV PYTHONUNBUFFERED=1

   WORKDIR /app

   # Create a non-privileged user that the app will run under.
   # See https://docs.docker.com/go/dockerfile-user-best-practices/
   ARG UID=10001
   RUN adduser \
       --disabled-password \
       --gecos "" \
       --home "/nonexistent" \
       --shell "/sbin/nologin" \
       --no-create-home \
       --uid "${UID}" \
       appuser

   # Download dependencies as a separate step to take advantage of Docker's    caching.
   # Leverage a cache mount to /root/.cache/pip to speed up subsequent builds.
   # Leverage a bind mount to requirements.txt to avoid having to copy them into
   # into this layer.
   RUN --mount=type=cache,target=/root/.cache/pip \
       --mount=type=bind,source=requirements.txt,target=requirements.txt \
       python -m pip install -r requirements.txt

   # Switch to the non-privileged user to run the application.
   USER appuser

   # Copy the source code into the container.
   COPY . .

   # Expose the port that the application listens on.
   EXPOSE 8001

   # Run the application.
   CMD python3 -m uvicorn app:app --host=0.0.0.0 --port=8001
   ```

   Create a file named `compose.yaml` with the following contents.

   ```yaml {collapse=true,title=compose.yaml}
   # Comments are provided throughout this file to help you get started.
   # If you need more help, visit the Docker Compose reference guide at
   # https://docs.docker.com/go/compose-spec-reference/

   # Here the instructions define your application as a service called "server".
   # This service is built from the Dockerfile in the current directory.
   # You can add other services your application may depend on here, such as a
   # database or a cache. For examples, see the Awesome Compose repository:
   # https://github.com/docker/awesome-compose
   services:
     server:
       build:
         context: .
       ports:
         - 8001:8001
   # The commented out section below is an example of how to define a PostgreSQL
   # database that your application can use. `depends_on` tells Docker Compose to
   # start the database before your application. The `db-data` volume persists the
   # database data between container restarts. The `db-password` secret is used
   # to set the database password. You must create `db/password.txt` and add
   # a password of your choosing to it before running `docker compose up`.
   #     depends_on:
   #       db:
   #         condition: service_healthy
   #   db:
   #     image: postgres
   #     restart: always
   #     user: postgres
   #     secrets:
   #       - db-password
   #     volumes:
   #       - db-data:/var/lib/postgresql/data
   #     environment:
   #       - POSTGRES_DB=example
   #       - POSTGRES_PASSWORD_FILE=/run/secrets/db-password
   #     expose:
   #       - 5432
   #     healthcheck:
   #       test: [ "CMD", "pg_isready" ]
   #       interval: 10s
   #       timeout: 5s
   #       retries: 5
   # volumes:
   #   db-data:
   # secrets:
   #   db-password:
   #     file: db/password.txt
   ```

   Create a file named `.dockerignore` with the following contents.

   ```text {collapse=true,title=".dockerignore"}
   # Include any files or directories that you don't want to be copied to your
   # container here (e.g., local build artifacts, temporary files, etc.).
   #
   # For more help, visit the .dockerignore file reference guide at
   # https://docs.docker.com/go/build-context-dockerignore/

   **/.DS_Store
   **/__pycache__
   **/.venv
   **/.classpath
   **/.dockerignore
   **/.env
   **/.git
   **/.gitignore
   **/.project
   **/.settings
   **/.toolstarget
   **/.vs
   **/.vscode
   **/*.*proj.user
   **/*.dbmdl
   **/*.jfm
   **/bin
   **/charts
   **/docker-compose*
   **/compose.y*ml
   **/Dockerfile*
   **/node_modules
   **/npm-debug.log
   **/obj
   **/secrets.dev.yaml
   **/values.dev.yaml
   LICENSE
   README.md
   ```

   Create a file named `.gitignore` with the following contents.

   ```text {collapse=true,title=".gitignore"}
   # Byte-compiled / optimized / DLL files
   __pycache__/
   *.py[cod]
   *$py.class

   # C extensions
   *.so

   # Distribution / packaging
   .Python
   build/
   develop-eggs/
   dist/
   downloads/
   eggs/
   .eggs/
   lib/
   lib64/
   parts/
   sdist/
   var/
   wheels/
   share/python-wheels/
   *.egg-info/
   .installed.cfg
   *.egg
   MANIFEST

   # Unit test / coverage reports
   htmlcov/
   .tox/
   .nox/
   .coverage
   .coverage.*
   .cache
   nosetests.xml
   coverage.xml
   *.cover
   *.py,cover
   .hypothesis/
   .pytest_cache/
   cover/

   # PEP 582; used by e.g. github.com/David-OConnor/pyflow and github.com/pdm-project/pdm
   __pypackages__/

   # Environments
   .env
   .venv
   env/
   venv/
   ENV/
   env.bak/
   venv.bak/
   ```

   {{< /tab >}}
   {{< /tabs >}}

## Add a local database and persist data

You can use containers to set up local services, like a database. In this section, you'll update the `compose.yaml` file to define a database service and a volume to persist data.

In the cloned repository's directory, open the `compose.yaml` file in an IDE or text editor. `docker init` handled creating most of the instructions, but you'll need to update it for your unique application.

In the `compose.yaml` file, you need to uncomment all of the database instructions. In addition, you need to add the database password file as an environment variable to the server service and specify the secret file to use .

The following is the updated `compose.yaml` file.

```yaml {hl_lines="7-43"}
services:
  server:
    build:
      context: .
    ports:
      - 8001:8001
    environment:
      - POSTGRES_SERVER=db
      - POSTGRES_USER=postgres
      - POSTGRES_DB=example
      - POSTGRES_PASSWORD_FILE=/run/secrets/db-password
    depends_on:
      db:
        condition: service_healthy
    secrets:
      - db-password
  db:
    image: postgres
    restart: always
    user: postgres
    secrets:
      - db-password
    volumes:
      - db-data:/var/lib/postgresql/data
    environment:
      - POSTGRES_DB=example
      - POSTGRES_PASSWORD_FILE=/run/secrets/db-password
    expose:
      - 5432
    healthcheck:
      test: ["CMD", "pg_isready"]
      interval: 10s
      timeout: 5s
      retries: 5
volumes:
  db-data:
secrets:
  db-password:
    file: db/password.txt
```

> [!NOTE]
>
> To learn more about the instructions in the Compose file, see [Compose file
> reference](/reference/compose-file/).

Before you run the application using Compose, notice that this Compose file specifies a `password.txt` file to hold the database's password. You must create this file as it's not included in the source repository.

In the cloned repository's directory, create a new directory named `db` and inside that directory create a file named `password.txt` that contains the password for the database. Using your favorite IDE or text editor, add the following contents to the `password.txt` file.

```text
mysecretpassword
```

Save and close the `password.txt` file.

You should now have the following contents in your `python-docker-dev-example`
directory.

```text
├── python-docker-dev-example/
│ ├── db/
│ │ └── password.txt
│ ├── app.py
│ ├── config.py
│ ├── requirements.txt
│ ├── .dockerignore
│ ├── .gitignore
│ ├── compose.yaml
│ ├── Dockerfile
│ ├── README.Docker.md
│ └── README.md
```

Now, run the following `docker compose up` command to start your application.

```console
$ docker compose up --build
```

Now test your API endpoint. Open a new terminal then make a request to the server using the curl commands:

Let's create an object with a post method

```console
$ curl -X 'POST' \
  'http://localhost:8001/heroes/' \
  -H 'accept: application/json' \
  -H 'Content-Type: application/json' \
  -d '{
  "id": 1,
  "name": "my hero",
  "secret_name": "austing",
  "age": 12
}'
```

You should receive the following response:

```json
{
  "age": 12,
  "id": 1,
  "name": "my hero",
  "secret_name": "austing"
}
```

Let's make a get request with the next curl command:

```console
curl -X 'GET' \
  'http://localhost:8001/heroes/' \
  -H 'accept: application/json'
```

You should receive the same response as above because it's the only one object we have in database.

```json
{
  "age": 12,
  "id": 1,
  "name": "my hero",
  "secret_name": "austing"
}
```

Press `ctrl+c` in the terminal to stop your application.

## Automatically update services

Use Compose Watch to automatically update your running Compose services as you
edit and save your code. For more details about Compose Watch, see [Use Compose
Watch](/manuals/compose/how-tos/file-watch.md).

Open your `compose.yaml` file in an IDE or text editor and then add the Compose
Watch instructions. The following is the updated `compose.yaml` file.

```yaml {hl_lines="17-20"}
services:
  server:
    build:
      context: .
    ports:
      - 8001:8001
    environment:
      - POSTGRES_SERVER=db
      - POSTGRES_USER=postgres
      - POSTGRES_DB=example
      - POSTGRES_PASSWORD_FILE=/run/secrets/db-password
    depends_on:
      db:
        condition: service_healthy
    secrets:
      - db-password
    develop:
      watch:
        - action: rebuild
          path: .
  db:
    image: postgres
    restart: always
    user: postgres
    secrets:
      - db-password
    volumes:
      - db-data:/var/lib/postgresql/data
    environment:
      - POSTGRES_DB=example
      - POSTGRES_PASSWORD_FILE=/run/secrets/db-password
    expose:
      - 5432
    healthcheck:
      test: ["CMD", "pg_isready"]
      interval: 10s
      timeout: 5s
      retries: 5
volumes:
  db-data:
secrets:
  db-password:
    file: db/password.txt
```

Run the following command to run your application with Compose Watch.

```console
$ docker compose watch
```

In a terminal, curl the application to get a response.

```console
$ curl http://localhost:8001
Hello, Docker!
```

Any changes to the application's source files on your local machine will now be immediately reflected in the running container.

Open `python-docker-dev-example/app.py` in an IDE or text editor and update the `Hello, Docker!` string by adding a few more exclamation marks.

```diff
-    return 'Hello, Docker!'
+    return 'Hello, Docker!!!'
```

Save the changes to `app.py` and then wait a few seconds for the application to rebuild. Curl the application again and verify that the updated text appears.

```console
$ curl http://localhost:8001
Hello, Docker!!!
```

Press `ctrl+c` in the terminal to stop your application.

## Summary

In this section, you took a look at setting up your Compose file to add a local
database and persist data. You also learned how to use Compose Watch to automatically rebuild and run your container when you update your code.

Related information:

- [Compose file reference](/reference/compose-file/)
- [Compose file watch](/manuals/compose/how-tos/file-watch.md)
- [Multi-stage builds](/manuals/build/building/multi-stage.md)

## Next steps

In the next section, you'll learn how you can locally test and debug your workloads on Kubernetes before deploying.