Dipping my toe into Mercurial …

Supports Mercurial 5.6+ and Python 3.6+!
Keeps support for Python 2.7!
No external dependencies other than Mercurial and Python!
Optionally uses SQLite database for faster blob imports!
Available on PiPy.org!

https://roy.marples.name/hg/
https://roy.marples.name/hg/hg-fastimport/
https://roy.marples.name/projects/hg-fastimport/
https://roy.marples.name/projects/hg-fastimport/downloads/
https://pypi.org/project/hg-fastimport/
https://www.mercurial-scm.org/wiki/FastImportExtension