Python language-specific guide

This guide explains how to containerize Python applications using Docker.

Acknowledgment
This guide is a community contribution. Docker would like to thank Esteban Maya and Igor Aleksandrov for their contribution to this guide.

The Python language-specific guide teaches you how to containerize a Python application using Docker. In this guide, you’ll learn how to:

Containerize and run a Python application
Set up a local environment to develop a Python application using containers
Lint, format, typing and best practices

Start by containerizing an existing Python application.

Containerize a Python application

Prerequisites

You have installed the latest version of Docker Desktop.

Containerizing your application means packaging it together with its dependencies, configuration, and runtime into a single portable unit called a container image. Running that image creates a container, an isolated process that behaves the same on any machine, whether it's your laptop, a CI runner, or a production server.

In this section, you'll containerize a simple FastAPI web application. You'll write a Dockerfile that describes how to build the image, add a compose.yaml file that defines how Docker runs your container, and then build and start the application with one command.

You'll use Docker Hardened Images as the base. These are minimal, secure Python images maintained by Docker.

Create the application

The sample application is a minimal FastAPI service with a single endpoint that returns a JSON greeting. Create the following files in a new python-docker-example directory. To create all the files at once, switch to the Scaffold script tab in the file browser and copy the shell command.

python-docker-example

# A minimal FastAPI application.
# The root endpoint (GET /) returns a JSON "Hello World" response.
# See https://fastapi.tiangolo.com/ for the framework reference.

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
async def root():
    return {"message": "Hello World"}

# Python package dependencies for the application, pinned for reproducible builds.
# See https://pip.pypa.io/en/stable/reference/requirements-file-format/

fastapi==0.115.12
uvicorn==0.34.3

# Files and directories that Git should ignore. This is the standard Python
# template covering bytecode, build artifacts, virtual environments, and IDE
# settings. See https://git-scm.com/docs/gitignore for syntax reference.

# 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/

# Secrets
db/password.txt

Overwrites existing files with the same names. Run from the parent of your project directory.

mkdir python-docker-example && cd python-docker-example
cat > app.py <<'__DOCKER_DOCS_SCAFFOLD_EOF__'
# A minimal FastAPI application.
# The root endpoint (GET /) returns a JSON "Hello World" response.
# See https://fastapi.tiangolo.com/ for the framework reference.

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
async def root():
    return {"message": "Hello World"}
__DOCKER_DOCS_SCAFFOLD_EOF__
cat > requirements.txt <<'__DOCKER_DOCS_SCAFFOLD_EOF__'
# Python package dependencies for the application, pinned for reproducible builds.
# See https://pip.pypa.io/en/stable/reference/requirements-file-format/

fastapi==0.115.12
uvicorn==0.34.3
__DOCKER_DOCS_SCAFFOLD_EOF__
cat > .gitignore <<'__DOCKER_DOCS_SCAFFOLD_EOF__'
# Files and directories that Git should ignore. This is the standard Python
# template covering bytecode, build artifacts, virtual environments, and IDE
# settings. See https://git-scm.com/docs/gitignore for syntax reference.

# 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/

# Secrets
db/password.txt
__DOCKER_DOCS_SCAFFOLD_EOF__

# Write files as UTF-8 without BOM. Works on Windows PowerShell 5.1 and PowerShell 7+.
function WriteFile([string]$Path, [string]$Content) {
    $full = Join-Path -Path (Get-Location).ProviderPath -ChildPath $Path
    [System.IO.File]::WriteAllText($full, $Content, [System.Text.UTF8Encoding]::new($false))
}

New-Item -ItemType Directory -Force -Path python-docker-example | Out-Null
Set-Location python-docker-example
WriteFile 'app.py' @'
# A minimal FastAPI application.
# The root endpoint (GET /) returns a JSON "Hello World" response.
# See https://fastapi.tiangolo.com/ for the framework reference.

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
async def root():
    return {"message": "Hello World"}
'@
WriteFile 'requirements.txt' @'
# Python package dependencies for the application, pinned for reproducible builds.
# See https://pip.pypa.io/en/stable/reference/requirements-file-format/

fastapi==0.115.12
uvicorn==0.34.3
'@
WriteFile '.gitignore' @'
# Files and directories that Git should ignore. This is the standard Python
# template covering bytecode, build artifacts, virtual environments, and IDE
# settings. See https://git-scm.com/docs/gitignore for syntax reference.

# 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/

# Secrets
db/password.txt
'@

If you already have Python installed and want to verify the app works before containerizing it, you can run it locally:

$ python3 -m venv .venv
$ source .venv/bin/activate
$ pip install -r requirements.txt
$ uvicorn app:app --reload

Note
On Windows, activate the virtual environment with .venv\Scripts\activate instead of source .venv/bin/activate.

If you don't have Python installed, skip ahead to the next section. The remaining steps run the application in a container, with no local Python required.

Create the Docker assets

Sign in to the DHI registry so Docker can pull the Python base images during the build. The available Python images are listed in the catalog.

$ docker login dhi.io

Add the following three files to your python-docker-example directory. The Dockerfile describes how to build the image, compose.yaml defines how Docker runs the container, and .dockerignore keeps unwanted files out of the build context.

Tip
Gordon, Docker's AI assistant, can generate Docker assets for your project. Ask Gordon to create a Dockerfile, Compose file, and .dockerignore tailored to your application.

python-docker-example

# A minimal FastAPI application.
# The root endpoint (GET /) returns a JSON "Hello World" response.
# See https://fastapi.tiangolo.com/ for the framework reference.

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
async def root():
    return {"message": "Hello World"}

# Python package dependencies for the application, pinned for reproducible builds.
# See https://pip.pypa.io/en/stable/reference/requirements-file-format/

fastapi==0.115.12
uvicorn==0.34.3

# 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/

# This Dockerfile uses Docker Hardened Images (DHI) for enhanced security.
# For more information, see https://docs.docker.com/dhi/

# Use the dev image to build and install dependencies.
FROM dhi.io/python:3.12-dev AS builder

WORKDIR /app

RUN python3 -m venv /venv
ENV PATH="/venv/bin:$PATH"

# 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
# this layer.
RUN --mount=type=cache,target=/root/.cache/pip \
    --mount=type=bind,source=requirements.txt,target=requirements.txt \
    pip install -r requirements.txt

# Use the minimal runtime image. It runs as nonroot by default.
FROM dhi.io/python:3.12

WORKDIR /app

What can I help you with?

Python language-specific guide

Containerize a Python application

Prerequisites

Overview

Create the application

Create the Docker assets