Rollback

This is a simple Pythonic mechanism for rolling back multiple operations in a predictable way, usable as a context manager or a standalone instance (see Example usage). By default, errors are re-raised, but an explicit mode or call must be supplied to trigger a rollback. Valid modes are:

• onError Boolean when True will roll back if an error is raised
• onSuccess Boolean when True will roll back if an error is not raised

Both modes can be set to True to always rollback. A rollback can also be triggered manually by calling doRollback. Note that multiple calls to doRollback will only call the rollback steps once.

Errors can be supressed by setting raiseError to False. Note that errors from rollback steps will not be surpressed, regardless of the raiseError setting.

If a rollback is triggered, each step is called in a last in, first out order (LIFO). That is, the most recently added step is called first, the first step is called last.

Compatibility

Rollback has no external dependencies and is regularly tested with all currently supported versions of cPython.

Installation

Install from source:

python setup.py install

Install from PyPI:

pip install rollback

Example usage

from __future__ import print_function

from rollback import Rollback

# *always* rollback after exiting block, letting any error be re-raised
with Rollback(onError=True, onSuccess=True) as rollback:
  print('do a1')
  rollback.addStep(print, 'undo a1')
  print('do a2')
  rollback.addStep(print, 'undo a2')

# rollback *only* if *no* error is raised, letting any error be re-raised
with Rollback(onSuccess=True) as rollback:
  print('do b1')
  rollback.addStep(print, 'undo b1')
  print('do b2')
  rollback.addStep(print, 'undo b2')

# rollback manually
with Rollback() as rollback:
  print('do c1')
  rollback.addStep(print, 'undo c1')
  print('do c2')
  rollback.addStep(print, 'undo c2')
  rollback.doRollback()

# rollback *only* if an error is raised, suppressing the error
with Rollback(onError=True, raiseError=False) as rollback:
  print('do d1')
  rollback.addStep(print, 'undo d1')
  print('do d2')
  rollback.addStep(print, 'undo d2')
  raise RuntimeError('this is not re-raised')

# rollback *only* if an error is raised, letting the error be re-raised
with Rollback(onError=True) as rollback:
  print('do e1')
  rollback.addStep(print, 'undo e1')
  print('do e2')
  rollback.addStep(print, 'undo e2')
  raise RuntimeError('this is re-raised')

Produces output:

do a1
do a2
undo a2
undo a1
do b1
do b2
undo b2
undo b1
do c1
do c2
undo c2
undo c1
do d1
do d2
undo d2
undo d1
do e1
do e2
undo e2
undo e1
Traceback (most recent call last):
  File "example.py", line 41, in <module>
    raise RuntimeError('this is re-raised')
RuntimeError: this is re-raised