@mitsuhiko The click._termui_impl.ProgressBar is a wonderful and magical piece of code.

There are cases though where subclassing this can be needed such as providing a few defaults progress messages such as on enter or exit of the context manager for intro and summaries.

This is especially useful to avoid otherwise naughty code mixing progress reporting and actual processing

Nothing prohibits this of course, but if it were made API, subclassing would benefit from a tad more stability with new upgrades. The overall interface of the class has been rather stable for about one year now with only a minor change to support manually updating more than one step at a time....

So IMHO this would benefit to be exposed in a non _ underscore module.