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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 _ycbcr2l(self, mode):
 """Convert from YCbCr to L. """

        self._check_modes(("YCbCr", "YCbCrA"))

        self.channels = [self.channels[0]] + self.channels[3:]
        if self.fill_value is not None:
            self.fill_value = [self.fill_value[0]] + self.fill_value[3:]
        self.mode = mode