code: def gradient_black(
              self, text=None, fore=None, back=None, style=None,
              start=None, step=1, reverse=False,
              linemode=True, movefactor=2, rgb_mode=False):
          
          gradargs = {
              'step': step,
              'fore': fore,
              'back': back,
              'style': style,
              'reverse': reverse,
              'rgb_mode': rgb_mode,
          }
  
          if linemode:
              gradargs['movefactor'] = 2 if movefactor is None else movefactor
              method = self._gradient_black_lines
          else:
              method = self._gradient_black_line
  
          if text:
              return self.__class__(
                  ''.join((
                      self.data or '',
                      method(
                          text,
                          start or (255 if reverse else 232),
                          **gradargs)
                  ))
              )
  
          # Operating on self.data.
          return self.__class__(
              method(
                  self.stripped(),
                  start or (255 if reverse else 232),
                  **gradargs)
          )
docs: Return a black and white gradient.
              Arguments:
                  text       : String to colorize.
                               This will always be greater than 0.
                  fore       : Foreground color, background will be gradient.
                  back       : Background color, foreground will be gradient.
                  style      : Name of style to use for the gradient.
                  start      : Starting 256-color number.
                               The `start` will be adjusted if it is not within
                               bounds.
                               This will always be > 15.
                               This will be adjusted to fit within a 6-length
                               gradient, or the 24-length black/white gradient.
                  step       : Number of characters to colorize per color.
                               This allows a "wider" gradient.
                  linemode   : Colorize each line in the input.
                               Default: True
                  movefactor : Factor for offset increase on each line when
                               using linemode.
                               Minimum value: 0
                               Default: 2
                  rgb_mode   : Use true color (rgb) method and codes.