step decorators permalink

conditional execution, looping & error handling for any step permalink

Complex steps have various optional step decorators that change how or if a step is run. You decorate your step’s core function with these extra behavioral attributes.

You can set any decorator on any step in your pipeline in any combination.

Don’t bother specifying these unless you want to deviate from the default values. If you don’t need any decorators for your step, you might as well save yourself some typing and use the step in simple mode instead by just specifying the bare step name.

  - name: my.package.another.module
    description: Optional description is for humans.
                 Any yaml-escaped text that makes your life easier.
                 Outputs to console during run-time.
    comment: Optional comments for pipeline developers. Like code comments.
             Does NOT output to console during run.
    in: # optional. Add these parameters to context for this step.
        # these key-value pairs only in scope for this step.
      parameter1: value1
      parameter2: value2
    foreach: [] # optional. Repeat the step once for each item in this list.
    onError: # optional. Custom Error Info to add to error if step fails.
      code: 111 # you can also use custom elements for your custom error.
      description: arb description here
    retry: # optional. Retry step until it doesn't raise an error.
      max: 1 # max times to retry. integer. Defaults None (infinite).
      sleep: 0 # sleep between retries, in seconds. Decimals allowed. Defaults 0.
      stopOn: ['ValueError', 'MyModule.SevereError'] # Stop retry on these errors. Defaults None (retry all).
      retryOn: ['TimeoutError'] # Only retry these errors. Defaults None (retry all).
    run: True # optional. Run this step if True, skip step if False. Defaults to True if not specified.
    skip: False # optional. Skip this step if True, run step if False. Defaults to False if not specified.
    swallow: False # optional. Swallow any errors raised by the step. Defaults to False if not specified.
    while: # optional. repeat step until stop is True or max iterations reached.
      stop: '{keyhere}' # loop until this evaluates True.
      max: 1 # max loop iterations to run. integer. Defaults None (infinite).
      sleep: 0 # sleep between iterations, in seconds. Decimals allowed. Defaults 0.
      errorOnMax: False # raise error if you reach max. Defaults False.

All step decorators support substitutions. This means you can dynamically use python expressions & token substitution strings that pypyr will interpret at runtime against changeable context values.

You can use py strings for dynamic boolean conditions like len(key) > 0.

If there are no looping decorators, the step will execute once by default, unless the conditional decorators skip the step.

If all of this sounds complicated, don’t panic! If you don’t bother with any of these the step will just run once by default.

bool evaluation permalink

Note that for all bool values, the standard Python truth value testing rules apply.

Simply put, this means that 1, TRUE, True and true will be True.

None/Empty, 0,'', [], {} will be False.

If pypyr finds a string where it expects a boolean, e.g on run, skip or swallow, it will interpret case insensitive string "true", "1" & "1.0" as boolean True. All other string values, including empty string, evaluate to False.

This is generally not what typical programming languages do on a strict string truthy, where any given string value other than null/empty will evaluate True, but more often than not within the context of a pipeline it saves you some footwork specially having to cast strings to booleans first.

order of precedence permalink

Decorators can interplay, meaning that the sequence of evaluation is important.

  • run or skip controls whether a step should execute on any given loop iteration, without affecting continued loop iteration.
  • run could be True but if skip is True it will still skip the step.
  • A step can run multiple times in a foreach loop for each iteration of a while loop.
  • swallow can evaluate dynamically inside a loop to decide whether to swallow an error or not on a particular iteration.
  • swallow can swallow an error AFTER retry exhausted max attempts.
in # in evals once and only once at the beginning of step
  -> while # everything below loops inside while
    -> foreach # everything below loops inside foreach
      -> run # evals dynamically on each loop iteration
       -> skip # evals dynamically on each loop iteration after run
        -> retry # repeats step execution until no error
          [>>>actual step execution here<<<]
        -> swallow # evaluates dynamically on each loop iteration

decorator listing permalink

  • comment

    Annotations for pipeline authors.

    comment: arb text
  • description

    Descriptive text that prints to output when step runs.

    description: text to print to output
  • foreach

    Repeat step for each item in list.

    foreach: ["one", "two", "three"]
  • in

    Add arguments to context for the current step.

      key: value
      anotherkey: anothervalue
  • onError

    Add custom error data on step error.

      code: 123
      description: arb text here
  • retry

    Retry step until it succeeds.

      max: 1 
      sleep: 2
      stopOn: ['ValueError', 'MyModule.SevereError']
      retryOn: ['TimeoutError']
  • run

    Run this step only if condition True.

    run: False
  • skip

    Skip this step if condition True.

      skip: True
  • swallow

    Swallow step error & continue with pipeline.

    swallow: True
  • while

    Repeat step until stop condition is True or up to the maximum iteration count.

      stop: '{keyhere}'
      max: 3
      sleep: 1.5
      errorOnMax: True
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