date(chunks.bytes)

The ``update()`` method also takes an optional value specifying the
``current_item`` at the new position. This is useful when used
together with ``item_show_func`` to customize the output for each
manual step::

    with click.progressbar(
        length=total_size,
        label='Unzipping archive',
        item_show_func=lambda a: a.filename
    ) as bar:
        for archive in zip_file:
            archive.extract()
            bar.update(archive.size, archive)

:param iterable: an iterable to iterate over.  If not provided the length
                 is required.
:param length: the number of items to iterate over.  By default the
               progressbar will attempt to ask the iterator about its
               length, which might or might not work.  If an iterable is
               also provided this parameter can be used to override the
               length.  If an iterable is not provided the progress bar
               will iterate over a range of that length.
:param label: the label to show next to the progress bar.
:param hidden: hide the progressbar. Defaults to ``False``. When no tty is
    detected, it will only print the progressbar label. Setting this to
    ``False`` also disables that.
:param show_eta: enables or disables the estimated time display.  This is
                 automatically disabled if the length cannot be
                 determined.
:param show_percent: enables or disables the percentage display.  The
                     default is `True` if the iterable has a length or
                     `False` if not.
:param show_pos: enables or disables the absolute position display.  The
                 default is `False`.
:param item_show_func: A function called with the current item which
    can return a string to show next to the progress bar. If the
    function returns ``None`` nothing is shown. The current item can
    be ``None``, such as when entering and exiting the bar.
:param fill_char: the character to use to show the filled part of the
                  progress bar.
:param empty_char: the character to use to show the non-filled part of
                   the progress bar.
:param bar_template: the format string to use as template for the bar.
                     The parameters in it are ``label`` for the label,
                     ``bar`` for the progress bar and ``info`` for the
                     info section.
:param info_sep: the separator between multiple info items (eta etc.)
:param width: the width of the progress bar in characters, 0 means full
              terminal width
:param file: The file to write to. If this is not a terminal then
    only the label is printed.
:param color: controls if the terminal supports ANSI colors or not.  The
              default is autodetection.  This is only needed if ANSI
              codes are included anywhere in the progress bar output
              which is not the case by default.
:param update_min_steps: Render only when this many updates have
    completed. This allows tuning for very fast iterators.

.. versionadded:: 8.2
    The ``hidden`` argument.

.. versionchanged:: 8.0
    Output is shown even if execution time is less than 0.5 seconds.

.. versionchanged:: 8.0
    ``item_show_func`` shows the current item, not the previous one.

.. versionchanged:: 8.0
    Labels are echoed if the output is not a TTY. Reverts a change
    in 7.0 that removed all output.

.. versionadded:: 8.0
   The ``update_min_steps`` parameter.

.. versionadded:: 4.0
    The ``color`` parameter and ``update`` method.

.. versionadded:: 2.0
r