checkpoint_logger is a simple checkpoint logger written in python. It writes checkpoints encoded in json into a file. On startup it can read existing checkpoints and rebuild state.

Here's an example of how to use it:

First create an instance of checkpoint_logger. You must pass it a directory. It creates a subdirectory called .checkpoint under the directory you provided. This is where it stores the files with the checkpoints.

>>> from checkpoint import Checkpoint
>>> x = Checkpoint("/tmp")

Next, create a checkpoint log key. A key corresponds to a checkpoint stream. In the current implementation it is a file. Writes to a given key are not thread safe and external synchronization is expected. Using separate keys, multiple threads can log events without needing synchronization.

>>> x.createCheckpointLog("test_key")

Write a few checkpoints. The first parameter is the checkpoint log key you created above. The second argument is an object whose state got modified and the third is the mutation itself. In the example below, the object "photo123" was first uploaded and then added to an album. The objects and events can be arbitrary strings and are defined by the user. Internally, the library writes the key-value pair encoded in json to the file corresponding to the checkpoint log key specified. The internal in memory state is also updated.

>>> x.writeCheckpoint("test_key", "photo123", "UPLOADED")
>>> x.writeCheckpoint("test_key", "photo123", "ADDED_TO_ALBUM")

To get the checkpoints for a given object, simply call getCheckpoints(). The checkpoints are guaranteed to be returned in the order that they were logged.

>>> x.getCheckpoints("photo123")
['UPLOADED', 'ADDED_TO_ALBUM']

To see all the checkpoint objects written call getCheckpointKeys()

>>> x.getCheckpointKeys()
['photo123']

Finally, when done, call releaseCheckpointLog() to release the checkpoint log key. This doesn't delete the underlying file; it merely tells the library that you are no longer interested in that key and that it can close the file.

>>> x.releaseCheckpointLog("test_key")