Generate a docker-compose.yml with mock services in Python

Build a docker-compose.yml string from a Python dict of service names and images, then write it to a file.

Easy Python 3.9+ Aug 9, 2026 Production deployment patterns 17 views 0 copies

docker compose yaml pyyaml configuration
Requires third-party packages — install first
pip install pyyaml

Python code

27 lines
Python 3.9+ 
import yaml
from pathlib import Path

def generate_mock_compose(services: dict) -> str:
    compose = {
        "version": "3.9",
        "services": {}
    }
    
    for name, image in services.items():
        compose["services"][name] = {
            "image": image,
            "container_name": f"mock-{name}",
            "restart": "unless-stopped"
        }
    
    return yaml.dump(compose, default_flow_style=False, sort_keys=False)

if __name__ == "__main__":
    services = {
        "web": "nginx:latest",
        "db": "postgres:16",
        "cache": "redis:7"
    }
    output = generate_mock_compose(services)
    print(output)
    Path("docker-compose.yml").write_text(output)

Output

stdout 
version: '3.9'
services:
  web:
    image: nginx:latest
    container_name: mock-web
    restart: unless-stopped
  db:
    image: postgres:16
    container_name: mock-db
    restart: unless-stopped
  cache:
    image: redis:7
    container_name: mock-cache
    restart: unless-stopped

How it works

The function takes a simple dict mapping service names to Docker images and builds a nested dict that mirrors the docker-compose.yml structure. yaml.dump converts that dict into YAML text with default_flow_style=False to keep it block-style and human-readable. Setting sort_keys=False preserves the insertion order so services appear in the same order as in the input. The Path.write_text call saves the YAML to disk, and the file is ready to use with docker compose up.

Common mistakes

  • Forgetting to quote the version number in the output — YAML 1.1 parses 3.9 as a float; use single quotes as shown.
  • Overwriting an existing docker-compose.yml without a backup or check — consider adding a `Path.exists()` guard.
  • Hardcoding the compose version when modern Docker supports `version` as optional and deprecated.
  • Assuming `yaml` is installed — it's not in the standard library; you must `pip install pyyaml`.

Variations

  1. Use `yaml.safe_dump` instead of `yaml.dump` for safer output when handling untrusted containers.
  2. Add environment variables or ports to the service dict for a richer mock setup.

Real-world use cases

  • Generating throwaway local environments for integration tests where real services can be replaced with mocks.
  • Scripting the creation of a compose file from a configuration file or CI variables for reproducible deployments.
  • Producing a template compose file that developers can edit before spinning up a group of related services.

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Run locally

This sample needs third-party packages, so it cannot run in the browser IDE. Copy the code above, install the packages shown at the top, then run it in your own Python environment.

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