Python runs

A Python run executes a script with python3. The script is the run's command. It suits a task that is more comfortable in Python than a shell: calling an API, reconciling state, or shaping data.

What runs

The script is written to a temporary file and run with python3, so multi-line scripts work unchanged. The working directory is the project checkout when the run sources a project. A dry run runs python3 -m py_compile, which checks syntax without executing the script.

How values reach the script

• Extra vars, including survey answers and template vars, arrive as SWITCHTENDER_VARS, a JSON object:

    import json, os
    vars = json.loads(os.environ.get("SWITCHTENDER_VARS", "{}"))
    region = vars.get("region", "us-east-1")
  

• Each var whose name a shell variable can hold and whose value is a string, a number, or a boolean also arrives on its own as SWITCHTENDER_VAR_<name>, which reads without parsing the JSON.

• An env credential's KEY=VALUE lines are set in the environment, read with os.environ.

• A token credential is set as SWITCHTENDER_TOKEN, ready to send as a bearer token.

• Credentials attached to the run's inventory arrive the same way.

Example

import json, os, urllib.request
vars = json.loads(os.environ.get("SWITCHTENDER_VARS", "{}"))
token = os.environ["SWITCHTENDER_TOKEN"]
req = urllib.request.Request(
    f"https://api.example.com/deploy/{vars['service']}",
    headers={"Authorization": f"Bearer {token}"}, method="POST")
print(urllib.request.urlopen(req).status)

See also Bash runs, Terraform runs, Go runs, and the tutorials.