acidfile module provides the ACIDFile object. This object can be used as a regular file object but instead of write one copy of the data, it will write several copies to disk in an ACID manner.

This algorithm was explained by Elvis Pfützenreuter in his blog post Achieving ACID transactions with common files.

Latest stable version can be found on PyPI.

acidfile is compatible with python 2.6, 2.7, 3.2, 3.3, 3.4 and pypy

Contribute:

Latest version can be installed via pip

$ pip install --upgrade acidfile

Clone this repository and install the develop requirements.

$ git clone https://github.com/nilp0inter/acidfile.git
$ cd acidfile
$ pip install -r requirements/develop.txt
$ python setup.py develop
$ tox

>>> from acidfile import ACIDFile

>>> myfile = ACIDFile('/tmp/myfile.txt', 'w')
>>> myfile.write(b'Some important data.')
>>> myfile.close()

At the close invocation two copies will be written to disk: myfile.txt.0 and below myfile.txt.1. Each one will have an creation timestamp and a HMAC signature.

>>> myfile = ACIDFile('/tmp/myfile.txt', 'r')
>>> print myfile.read()
'Some important data.'
>>> myfile.close()

If any of the files is damaged due to turning off without proper shutdown or disk failure, manipulation, etc. It will be detected by the internal HMAC and the other's file data would be used instead.

ACIDFile can (and should) be used as a regular context manager:

>>> with ACIDFile('/tmp/myfile.txt', 'w') as myfile:
...     myfile.write(b'Some important data.')

The number of inner copies of the data can be configured through the copies parameter.

The key used for compute and check the internal HMAC signature can be setted by the key parameter.

It's recommended to change that key in order to protect against fraud, making more difficult for a tamperer to put a fake file in place of the legitimate one.