Semaphore UI
Overview

Python

Create a Python template#

  1. Go to Task Templates and click New Template.
  2. Select Python as the app type.
  3. Configure it:
Field Description
Name A descriptive name for the template
Repository The repository containing your .py script
Playbook / Script Relative path to the script, e.g. scripts/deploy.py
Variable Groups Variable groups whose values are injected as environment variables
  1. Create, then Run.

Passing variables#

Variable group values arrive in the environment:

import os
 
target = os.environ.get("TARGET_HOST")
print(f"Deploying to {target}")

Secrets from the Secrets tab work the same way and stay out of the task log.

Python version and dependencies#

Semaphore uses whichever python3 is on PATH in the execution environment. How you control that depends on your install:

Install How to control it
Package or binary Install the required python3 on the host
Docker Build a custom image with the version you need
Docker, extra packages only Mount a requirements.txt at /etc/semaphore/requirements.txt — Semaphore runs pip3 install --upgrade -r on container start

The requirements.txt route is shared with Ansible collections that need Python libraries; see Install.

If different templates need conflicting dependency sets, give them separate runners rather than fighting one shared environment.

Rules of the road#

  • Scripts run non-interactively — nothing that waits on input().
  • Exit code 0 is success; anything else fails the task. An uncaught exception exits non-zero, which is the behaviour you want.
  • Write progress to stdout: it becomes the streamed task log, and it is what someone reads at 3am.

Next steps#

  • Shell / Bash — for the smaller jobs
  • Runners — isolating dependency sets
  • REST API — calling Semaphore from Python instead of the other way round
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