======================================== Show progress when the total isn't known

A percentage and an ETA both need a total to measure against -- neither means anything for a job whose length you can't compute in advance, such as scanning a filesystem or reading a stream.

.. demo:: howto/unknown-length

Pass max_value=progressbar.UnknownLength and include an AnimatedMarker (or another marker-style widget) so there is still something visibly moving even without a percentage to report. A Counter() widget still works normally here, since it just echoes value rather than computing a fraction of max_value.