lethe/lethe

lethe README

lethe is a Python module for git-based snapshotting.

lethe is intended as a mechanism for creating commits outside the standard git branching/tagging workflows. It is meant to enable additional use-cases without disrupting the standard workflows. Use cases include:

• Short-lived:
  • On-disk undo log
  • Syncing work-in-progress between computers before it's ready
• Long-lived:
  • lab notebook: Recording the code / configuration state that resulted in a given output
  • incremental backup: Space-efficient time-based backups of a codebase

Usage

Creating a commit from the command line

$ cd path/to/repo
$ lethe
122d058e375274a186c407f28602c3b14a2cab95

This effectively snapshots the current state of the repository (as would be seen by git add --all) and creates a new commit (122d058e375274a186c407f28602c3b14a2cab95) which points to it. The current branch and index are not changed.

Flags:

• -p my_parent_ref is used to provide "parent" refs which become the parents of the created commit. If a parent ref is a symbolic ref, both the provided ref and the ref it points to are used as parents. If not present, defaults to -p HEAD.
• -t ref/lethe/my_target_ref is used to provide "target" refs which will be created/updated to point to the created commit. If not present, defaults to adding an entry of the form -t refs/lethe/my_branch for each parent ref of the form refs/heads/my_branch, and -t refs/lethe/my/refpath for non-head refs of the form refs/my/refpath. All provided parent refs and any dereferenced parent refs are used to generate default target refs. If any of the target refs already exist, the commits they point to become parents of the created commit.
• -m "my message" sets the commit message for the snapshot. By default, "snapshot " is used.
• -r path/to/repo can be provided to specify a repository outside of the current working directory.

$ cd path/to/repo
$ git branch
* master
$ lethe

is equivalent to

lethe -r path/to/repo -p HEAD

or

lethe -r path/to/repo -p HEAD -p refs/heads/master -t refs/lethe/HEAD -t refs/lethe/master

Creating a commit programmatically

import lethe
REPO = '/path/to/repo'

commit_sha = lethe.snap(cwd=REPO)
tree_sha = lethe.get_tree(commit_sha, cwd=REPO)

print('Created new commit with hash ' + commit_sha + ' aka refs/lethe/HEAD')
print('Code (tree) state is ' + tree_sha)

Installation

Requirements:

• python 3 (written and tested with 3.6)
• git (accessible on the system PATH)

Install with pip:

pip3 install lethe