Add support for Amazon States Language "ResultSelector" in Task, Map …

[yoodan93]

Add ResultSelector support for Task, Map and Parallel states.

Issue #, if available: https://github.com/aws/aws-step-functions-data-science-sdk-python/issues/95

---

Description of changes

Adding new Amazon States Language payload template "ResultSelector" https://states-language.net/#payload-template This change allows user to define a result_selector which is used to define the effective result of a state.

Testing

• Added unit test for changes
• Manual test:

# Create a simple workflow containing a task state with `result_selector`
from stepfunctions.inputs import StepResult

step_result = StepResult()
step_result_placeholder = {
    'Output': step_result['output']
}

state_with_result_selector = Task(
    state_id='StartState',
    parameters={'Key': 'Value'},
    result_selector=step_result_placeholder,
    resource=<resource_arn>
)

workflow = Workflow(
    name="ResultSelector_Example",
    definition=state_with_result_selector,
    role=<workflow_execution_role>
)

# Execute the workflow and confirm it has completed successfully
workflow.execute()

Workflow definition:

{
    "StartAt": "StartState",
    "States": {
        "StartState": {
            "Parameters": {
                "Key": "Value"
            },
            "ResultSelector": {
                "Output.$": "$['output']"
            },
            "Resource": <resource_arn>,
            "Type": "Task",
            "End": true
        }
    }
}

---

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[milesgranger]

Any update with this? Would be fantastic to have! :+1:

[ca-nguyen]

Taking over to help merge @yoodan93 's PR Thank you for your review - will be addressing comments shortly

[ca-nguyen]

can you also add some details around testing

Added manual test details

at some point we should probably add some basic integ tests that exercise state machines and their support for ASL features. Presumably, we'll be adding more capabilities in the future. Probably not in scope for this PR, but worth thinking about sooner than later.

Agreed! let's do add integ tests in another PR

[wong-a]

Manual test: Generated a workflow with a Task with StepResult placeholder and executed successfully

This is very unspecific. Can you share the SDK code you used to generate that?

[ca-nguyen]

This is very unspecific. Can you share the SDK code you used to generate that?

Agreed - this is not sufficient information to reproduce the test. I provided more details in the Testing section of the PR description

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• CodeBuild project: AutoBuildProject6AEA49D1-sEHrOdk7acJc
• Commit ID: 6594b1c7412095c0a24f2daf502dbe5d85e003d6
• Result: SUCCEEDED
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[alesageProovStation]

Hi! Any plans on merging this PR soon? I'm writing a stepfunction state machine which requires this... Thanks.