To use a workaround for another bug, I had to first update GitPython. After updating withpip3 install --upgrade gitpython, which installed 2.1.3, the progress feature no longer functions correctly.

With this code:

import gitdef u(*args): print(args, flush=True)git.Repo.clone_from("git@bitbucket.org:....", ".", u)

While running it on a fairly large repository, I get the first few updates, upto:
(10, 16118.0, 16118.0, '') (which means compressing has completed)

But, then the next stage when it is downloading everything, which can take about 15 mins, there is no feedback until it has completed that stage, then all the missing feedback is sent at once, as if the feedback has gathered in a buffer and not sent until the current stage is complete.