pypyr pipeline with dependencies & idempotency

deps-example.yaml

# run this like follows:
# Run only the common/shared dependency:
# $ pypyr deps-example 
# 
# Run either my_task or another_task:
# $ pypyr deps-example my_task
# $ pypyr deps-example another_task
# 
# And to run both tasks:
# $ pypyr deps-example my_task another_task
context_parser: pypyr.parser.list
# steps is the standard entry point - this runs 1st
steps:
  - name: pypyr.steps.call
    description: -> common_setup - think of this as dependencies that have to run every time
    in:
      call: common_setup

  - name: pypyr.steps.call
    comment: optionally do extras like my_task or another_task after common
    run: '{argList}'
    in:
      call: '{argList}'

  - name: pypyr.steps.echo
    in:
      echoMe: done!

common_setup:
  - name: pypyr.steps.pyimport
    comment: you can import anything here
             we'll be using Path to check if file exists on disk to decide
             whether to run a step again or not for idempotency
    in:
      pyImport: from pathlib import Path

  - name: pypyr.steps.echo
    in:
      echoMe: common 1

  - name: pypyr.steps.echo
    in:
      echoMe: common 2

dep1:
# dep1 somewhat arbitrarily creates out/arb.txt
# dep1 will only create out/arb.txt ONCE, if file already exists will stop 
# and exit this step-group immediately without doing anything
  - name: pypyr.steps.stopstepgroup
    comment: exit this group is out/arb.txt already exists
    run: !py Path('out/arb.txt').exists()

  - name: pypyr.steps.cmd
    description: -> doing dep1
    in:
      cmd: mkdir -p out

  - name: pypyr.steps.cmd
    comment: each dependency can have multiple steps in it
    in:
      cmd: touch out/arb.txt

dep2:
# dep2 somewhat arbitrarily creates out/arb2.txt
# dep2 shows a different way of achieving idempotency:
# 1) when another_task calls dep2 it uses the `skip` decorator to skip group
# if out/arb.txt already exists
# 2) unlike dep1, dep2 does not itself check whether it should run or not.
# therefore it will ALWAYS run when my_task calls it - it's up to the caller
# to decide idempotent behavior
  - name: pypyr.steps.cmd
    description: -> doing dep2
    in:
      cmd: mkdir -p out

  - name: pypyr.steps.cmd
    comment: each dependency can have multiple steps in it
    in:
      cmd: touch out/arb2.txt

my_task:
  - name: pypyr.steps.call
    description: -> my_task calls dependencies dep1 & dep2 1st
    in:
      call: [dep1, dep2]

  - name: pypyr.steps.cmd
    description: -> now doing my_task stuff
    in:
      cmd: echo my_task stuff

another_task:
  - name: pypyr.steps.call
    comment: skip the dependency if out/arb2.txt exists already
    skip: !py Path('out/arb2.txt').exists()
    in:
      call: dep2

  - name: pypyr.steps.cmd
    in:
      cmd: echo another_task stuff