python-example-workflow.yaml

apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: python-example-
spec:
  entrypoint: main
  arguments:
    parameters:
      - name: value
        value: "1"
  templates:
    - name: main
      dag:
        tasks:
          - name: add-one
            template: add-one
            arguments:
              parameters:
                - name: value
                  value: "{{workflow.parameters.value}}"
          - name: print-sum
            template: print-sum
            dependencies:
              - add-one
            arguments:
              parameters:
                - name: sum
                  value: "{{tasks.add-one.outputs.parameters.sum}}"

    - name: add-one
      inputs:
        parameters:
          - name: value
      plugin:
        python:
          expression: |
            {"sum": int(parameters["value"]) + 1}
      outputs:
        parameters:
          - name: sum
            # you must specify "value" or "valueFrom", but what you specify does not matter
            valueFrom:
              supplied: { }

    - name: print-sum
      inputs:
        parameters:
          - name: sum
      container:
        image: argoproj/argosay:v2
        args:
          - echo
          - "{{inputs.parameters.sum}}"