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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _gradient_black_line( self, text, start, step=1, fore=None, back=None, style=None, reverse=False, rgb_mode=False):
 """ Yield colorized characters, within the 24-length black gradient. """

        if start < 232:
            start = 232
        elif start > 255:
            start = 255
        if reverse:
            codes = list(range(start, 231, -1))
        else:
            codes = list(range(start, 256))
        return ''.join((
            self._iter_text_wave(
                text,
                codes,
                step=step,
                fore=fore,
                back=back,
                style=style,
                rgb_mode=rgb_mode
            )
        ))