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Reusable actions

Like scripted actions, reusable actions are logical units of analytic code. However, whereas a scripted action is written to solve a problem for one study and must be copied-and-pasted to solve a similar problem for another study, a reusable action is written to solve a problem for several studies without copying-and-pasting between them. This makes reusable actions ideal for tasks that must be completed by several studies, such as producing cross-tabulations, summary statistics, or deciles charts.

Running reusable actions🔗

You can browse existing reusable actions at https://actions.opensafely.org. Although each is different, they have a common API. Consider the following extract from a study's project.yaml:

actions:
  generate_my_cohort:
    run: cohortextractor:latest generate_cohort --output-format=csv.gz
    outputs:
      highly_sensitive:
        cohort: output/input.csv.gz

  run_a_reusable_action:
    # We will run version `v1.0.0` of the reusable action called `a_reusable_action`.
    # The reusable action accepts an argument; in this case, a path to a file.
    run: a_reusable_action:v1.0.0 output/input.csv.gz
    # The reusable action accepts a configuration option;
    # in this case, an output format.
    config:
      output-format: PNG
    needs: [generate_my_cohort]
    outputs:
      moderately_sensitive:
        output: output/output_from_a_reusable_action.png

In the above extract, the run and config properties of run_a_reusable_action are the common API. The run property, which is required, describes how the reusable action is run. It comprises the name and the version of the reusable action, and, optionally, one or more arguments. The config property, which is optional, describes configuration options.

Developing reusable actions🔗

A reusable action is a public repo within the opensafely-actions organisation. It has a main branch, which is the release branch; versions are marked with tags. In the above extract from a study's project.yaml, for example, we will run version v1.0.0 of the reusable action called a_reusable_action.

The repo has the following minimal structure:

.
├── README.md
└── action.yaml

README.md contains information about the reusable action, which is displayed by https://actions.opensafely.org.

action.yaml contains a run command, which is composed of a runtime image (either python, r, or stata-mp) and an entry point. The entry point is a path to a script. For example:

run: python:latest python action/cli.py

Where action/cli.py is:

def main():
  print("A reusable action")

if __name__ == "__main__":
  main()

When developing a reusable action, just as when developing a scripted action, the action's dependencies are made available by the runtime; they are not made available by the action.

To develop a Python reusable action, consider using the python-action-template repo. This repo goes beyond the minimal structure, making it easier to develop a Python reusable action than starting from scratch.