DRY Patterns

ghagen definitions are plain code, so standard techniques for reducing duplication work naturally. This guide covers common patterns for keeping your workflow code concise and maintainable.

Job template functions

Define a function that returns a job to create reusable job templates:

Python

from ghagen import Job, Step, checkout

def lint_job(tool: str, cmd: str) -> Job:
return Job(
name=f"Lint ({tool})",
runs_on="ubuntu-latest",
steps=[
checkout(),
Step(name=tool, run=cmd),
],
)

Use it to stamp out multiple jobs without repeating the structure:

jobs = {
    "ruff": lint_job("Ruff", "ruff check ."),
    "mypy": lint_job("Mypy", "mypy src/"),
    "black": lint_job("Black", "black --check ."),
}

TypeScript

import { job, step } from "@ghagen/ghagen";
import type { JobModel } from "@ghagen/ghagen";

function lintJob(tool: string, cmd: string): JobModel {
return job({
name: `Lint (${tool})`,
runsOn: "ubuntu-latest",
steps: [
step({ uses: "actions/checkout@v4" }),
step({ name: tool, run: cmd }),
],
});
}

const jobs = {
ruff: lintJob("Ruff", "ruff check ."),
mypy: lintJob("Mypy", "mypy src/"),
black: lintJob("Black", "black --check ."),
};

You can parameterize anything — runner labels, Python versions, dependency install commands, or entire step lists.

Shared constants

Extract repeated values into variables to ensure consistency and simplify updates:

Python

RUNNER = "ubuntu-latest"
PYTHON_VERSION = "3.12"
CHECKOUT_ACTION = "actions/checkout@v4"
SETUP_PYTHON_ACTION = "actions/setup-python@v5"

Job(
    runs_on=RUNNER,
    steps=[
        Step(uses=CHECKOUT_ACTION),
        Step(uses=SETUP_PYTHON_ACTION, with_={"python-version": PYTHON_VERSION}),
    ],
)

TypeScript

import { job, step } from "@ghagen/ghagen";

const RUNNER = "ubuntu-latest";
const PYTHON_VERSION = "3.12";
const CHECKOUT_ACTION = "actions/checkout@v4";
const SETUP_PYTHON_ACTION = "actions/setup-python@v5";

job({
runsOn: RUNNER,
steps: [
step({ uses: CHECKOUT_ACTION }),
step({ uses: SETUP_PYTHON_ACTION, with_: { "python-version": PYTHON_VERSION } }),
],
});

When a new action version is released, update the constant in one place.

Loops

Use iteration to generate repetitive structures:

Python

services = ["api", "web", "worker"]

jobs = {
    f"build-{svc}": Job(
        name=f"Build {svc}",
        runs_on="ubuntu-latest",
        steps=[
            checkout(),
            Step(name="Build", run=f"docker build -t {svc} ./services/{svc}"),
        ],
    )
    for svc in services
}

This works equally well for generating step lists:

linters = [("ruff", "ruff check ."), ("mypy", "mypy src/")]

steps = [checkout()] + [
    Step(name=name, run=cmd) for name, cmd in linters
]

TypeScript

import { job, step } from "@ghagen/ghagen";

const services = ["api", "web", "worker"];

const jobs = Object.fromEntries(
services.map((svc) => [
`build-${svc}`,
job({
name: `Build ${svc}`,
runsOn: "ubuntu-latest",
steps: [
step({ uses: "actions/checkout@v4" }),
step({ name: "Build", run: `docker build -t ${svc} ./services/${svc}` }),
],
}),
])
);