unit [default: 'it'].
unit_scale  : bool or int or float, optional
    If 1 or True, the number of iterations will be printed with an
    appropriate SI metric prefix (k = 10^3, M = 10^6, etc.)
    [default: False]. If any other non-zero number, will scale
    `total` and `n`.
rate  : float, optional
    Manual override for iteration rate.
    If [default: None], uses n/elapsed.
bar_format  : str, optional
    Specify a custom bar string formatting. May impact performance.
    [default: '{l_bar}{bar}{r_bar}'], where
    l_bar='{desc}: {percentage:3.0f}%|' and
    r_bar='| {n_fmt}/{total_fmt} [{elapsed}<{remaining}, '
      '{rate_fmt}{postfix}]'
    Possible vars: l_bar, bar, r_bar, n, n_fmt, total, total_fmt,
      percentage, elapsed, elapsed_s, ncols, nrows, desc, unit,
      rate, rate_fmt, rate_noinv, rate_noinv_fmt,
      rate_inv, rate_inv_fmt, postfix, unit_divisor,
      remaining, remaining_s, eta.
    Note that a trailing ": " is automatically removed after {desc}
    if the latter is empty.
postfix  : *, optional
    Similar to `prefix`, but placed at the end
    (e.g. for additional stats).
    Note: postfix is usually a string (not a dict) for this method,
    and will if possible be set to postfix = ', ' + postfix.
    However other types are supported (#382).
unit_divisor  : float, optional
    [default: 1000], ignored unless `unit_scale` is True.
initial  : int or float, optional
    The initial counter value [default: 0].
colour  : str, optional
    Bar colour (e.g. 'green', '#00ff00').

Returns
-------
out  : Formatted meter and stats, ready to display.
g