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  4. retry

retry permalink

automatic retries permalink

Retries the step until it succeeds. If you do not set retry, pypyr will not retry the step automatically. When you do set retry, pypyr will retry whatever step it is without you having to do anything else.

The retry iteration counter is context['retryCounter']. You can use this as usual for any context value in a formatting string expression as {retryCounter}.

These are all the available configuration parameters for retry:

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).

All inputs support substitutions, so you can assign values to these properties dynamically at run-time.

If you reach max retry count while the step still errors, pypyr will raise the last error and stop further pipeline processing.

If you set swallow to True, pypyr will swallow the error after max retries exhausts.

retry with sleep permalink

Use sleep to pause in between retries. Sleep is a decimal with the unit seconds. If you do not set sleep, the default wait between retries is 0s.

# ./retry-sleep.yaml
steps:
  - name: pypyr.steps.echo
    in:
      echoMe: begin
  - name: pypyr.steps.assert
    comment: assert will fail until the 3rd retry.
             will sleep 0.5s between retries.
             on 3rd retry, step succeeds, and 
             pypyr proceeds to next step.
    retry:
      max: 4
      sleep: 0.5
    in:
      assert:
        this: !py retryCounter == 3
  - name: pypyr.steps.echo
    in:
      echoMe: end. you'll see me only after previous step succeeds.

$ pypyr retry-sleep
begin
retry: ignoring error because retryCounter < max.
ContextError: assert retryCounter == 3 evaluated to False.
retry: ignoring error because retryCounter < max.
ContextError: assert retryCounter == 3 evaluated to False.
end. you'll see me only after previous step succeeds.

infinite retry permalink

Set max to 0 or null for to retry indefinitely until the step succeeds.

It’s up to you to interrupt an infinite loop. If you’re using the cli, you can hit CTRL+C to interrupt and exit pypyr.

# ./retry-infinite.yaml
steps:
  - name: pypyr.steps.assert
    description: CTRL+C to exit
    comment: 0 or null means infinite retry.
             since sleep not set, will retry
             immediately with no delay between
             retries.
    in:
      assert:
          this: False
    retry:
      max: 0 # 0 or null means indefinitely
  - name: pypyr.steps.echo
    in:
      echoMe: this won't run because the previous step always errors.

$ pypyr retry-infinite
pypyr.steps.assert: CTRL+C to exit
retry: ignoring error because retryCounter < max.
ContextError: assert False evaluated to False.
retry: ignoring error because retryCounter < max.
ContextError: assert False evaluated to False
^C

$ echo $?
130

retry entire sequence of steps permalink

You can retry any step, whether it is your own or a built-in pypyr step. If you retry on a call step, you retry an entire sequence of steps inside a step-group. This lets you retry multiple steps as a unit.

# ./retry-call
steps:
  - name: pypyr.steps.echo
    in:
      echoMe: begin
  - name: pypyr.steps.call
    comment: all of retry_me will retry 3X if it returns an error.
    retry:
      max: 3
    in:
      call:
        groups: retry_me
  - name: pypyr.steps.echo
    in:
      echoMe: you won't see me, because the previous step always errs.

retry_me:
    - name: pypyr.steps.echo
      in:
        echoMe: "running retry {retryCounter}"
    - name: pypyr.steps.assert
      in:
        assert:
          this: False
    - name: pypyr.steps.echo
      in:
        echoMe: you won't see me, because the previous step always errs.

This will result in:

$ pypyr retry-call
begin
running retry 1
Error while running step pypyr.steps.assert at pipeline yaml line: 20, col: 7
retry: ignoring error because retryCounter < max
ContextError: assert False evaluated to False.
running retry 2
Error while running step pypyr.steps.assert at pipeline yaml line: 20, col: 7
retry: ignoring error because retryCounter < max
ContextError: assert False evaluated to False.
running retry 3
Error while running step pypyr.steps.assert at pipeline yaml line: 20, col: 7
Error while running step pypyr.steps.call at pipeline yaml line: 6, col: 5
Something went wrong. Will now try to run on_failure.

ContextError: assert False evaluated to False.

only retry specific error types permalink

When you set neither stopOn nor retryOn, all types of errors will retry. This is the default behavior.

If you specify stopOn, errors listed in stopOn will stop retry processing and raise an error. Errors not listed in stopOn will retry.

If you specify retryOn, ONLY errors listed in retryOn will retry.

max evaluates before stopOn and retryOn.

stopOn supersedes retryOn.

For builtin python errors, specify the bare error name for stopOn and retryOn, e.g ValueError, KeyError.

For all other errors, use module.errorname, e.g mypackage.mymodule.myerror

only retry on specific errors permalink

# ./retry-retryon.yaml
steps:
  - name: pypyr.steps.py
    description: this step will retry infinitely until the cmd does not return an error.
    comment: retries 1 & 2 raise ValueError, 
              retry 3 raise KeyError.
              KeyError is not in retryOn, so will quit step reporting failure.
    retry:
      # will ONLY retry these errors. All other stop processing.
      retryOn: ['KeyError', 'pypyr.errors.ContextError']
    in:
      pycode: |
              if context['retryCounter'] == 3:
                raise ValueError('this won't retry!')
              else:
                raise KeyError('this will retry')              
  - name: pypyr.steps.echo
    in:
      echoMe: this won't run because the previous step always errors.

This will result in:

 $ pypyr retry-retryon
this step will retry infinitely until the cmd does not return an error.
retry: ignoring error because retryCounter < max.
KeyError: 'this will retry'
retry: ignoring error because retryCounter < max.
KeyError: 'this will retry'
ValueError not in retryOn. Raising error and exiting retry.
Error while running step pypyr.steps.py at pipeline yaml line: 4, col: 7
Something went wrong. Will now try to run on_failure.

ValueError: Booom!

$ echo $?
255

stop processing on specific error type permalink

# ./retry-retrystopon
steps:
  - name: pypyr.steps.py
    description: this step will retry infinitely until the cmd does not return an error.
    retry:
      # will stop retry on these errors. All others will carry on retry processing.
      stopOn: ['ValueError', 'pypyr.errors.ContextError']
    in:
      pycode: |
              if context['retryCounter'] == 3:
                raise ValueError('this will STOP processing!')
              else:
                raise KeyError('this will retry')              
  - name: pypyr.steps.echo
    in:
      echoMe: this won't run because the previous step always errors.

This will result in:

$ pypyr retry-retrystopon
this step will retry infinitely until the cmd does not return an error.
retry: ignoring error because retryCounter < max.
KeyError: 'this will retry'
retry: ignoring error because retryCounter < max.
KeyError: 'this will retry'
ValueError in stopOn. Raising error and exiting retry.
Error while running step pypyr.steps.py at pipeline yaml line: 4, col: 7
Something went wrong. Will now try to run on_failure.

ValueError: this will STOP processing!

see also

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