for item in bar:
                do_something_with(item)

    Alternatively, if no iterable is specified, one can manually update the
    progress bar through the `update()` method instead of directly
    iterating over the progress bar.  The update method accepts the number
    of steps to increment the bar with::

        with progressbar(length=chunks.total_bytes) as bar:
            for chunk in chunks:
                process_chunk(chunk)
                bar.update(chunks.bytes)

    .. versionadded:: 2.0

    .. versionadded:: 4.0
       Added the `color` parameter.  Added a `update` method to the
       progressbar object.

    :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 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 the current item
                           next to the progress bar.  Note that the current
                           item can be `None`!
    :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.
    r