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Dag Conditional Parameters

Note

This example is a replication of an Argo Workflow example in Hera. The upstream example can be found here.

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from hera.expr import g
from hera.workflows import DAG, Parameter, Script, Task, Workflow


def heads():
    print("heads")


def tails():
    print("tails")


def flip_coin():
    import random

    print("heads" if random.randint(0, 1) == 0 else "tails")


def get_script(callable):
    return Script(
        name=callable.__name__.replace("_", "-"),
        source=callable,
        add_cwd_to_sys_path=False,
        image="python:alpine3.6",
    )


with Workflow(
    generate_name="dag-conditional-parameter-",
    entrypoint="main",
) as w:
    heads_template = get_script(heads)
    tails_template = get_script(tails)
    flip_coin_template = get_script(flip_coin)

    with DAG(name="main") as main_dag:
        flip_coin_task = Task(name="flip-coin", template=flip_coin_template)
        heads_task = Task(name="heads", template=heads_template)
        tails_task = Task(name="tails", template=tails_template)
        heads_task.on_other_result(flip_coin_task, "heads")
        tails_task.on_other_result(flip_coin_task, "tails")

        expression = g.tasks["flip-coin"].outputs.result == "heads"
        expression = expression.check(g.tasks.heads.outputs.result, g.tasks.tails.outputs.result)  # type: ignore
        main_dag.outputs = [Parameter(name="stepresult", value_from={"expression": str(expression)})]

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apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: dag-conditional-parameter-
spec:
  entrypoint: main
  templates:
  - name: heads
    script:
      image: python:alpine3.6
      source: print('heads')
      command:
      - python
  - name: tails
    script:
      image: python:alpine3.6
      source: print('tails')
      command:
      - python
  - name: flip-coin
    script:
      image: python:alpine3.6
      source: |-
        import random
        print('heads' if random.randint(0, 1) == 0 else 'tails')
      command:
      - python
  - name: main
    dag:
      tasks:
      - name: flip-coin
        template: flip-coin
      - name: heads
        depends: flip-coin
        template: heads
        when: '{{tasks.flip-coin.outputs.result}} == heads'
      - name: tails
        depends: flip-coin
        template: tails
        when: '{{tasks.flip-coin.outputs.result}} == tails'
    outputs:
      parameters:
      - name: stepresult
        valueFrom:
          expression: 'tasks[''flip-coin''].outputs.result == ''heads'' ? tasks.heads.outputs.result
            : tasks.tails.outputs.result'

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