Step 3: Give the bar a max_value

Without knowing how much work there is, a ProgressBar has nothing to divide the current value by, so it cannot show a percentage or estimate how long is left. This step tells it the total up front so it can show both.

"""Give the bar a `max_value` so it can show a percentage and an ETA.

Without one -- as in the previous step -- `ProgressBar` has no way to know
how much work is left, so it falls back to an indeterminate spinner
instead of a percentage.
"""

import time

import progressbar


def main() -> None:
    with progressbar.ProgressBar(max_value=100) as bar:
        for i in range(100):
            time.sleep(0.01)
            bar.update(i + 1)


if __name__ == '__main__':
    main()

The previous step’s ProgressBar() call took no arguments, so the bar rendered as an indeterminate display – there was no way to know how far through the work it was. Here the constructor gains a max_value=100 argument: progressbar.ProgressBar(max_value=100). Nothing else about the loop changes – bar.update(i + 1) is called exactly as before – but knowing the total lets the bar compute a percentage and an ETA from each update instead of just showing that something is happening.

Next: Step 4: Choose your own widgets.