def _grow_secondary(self, amt):
        """Will grow the focused client in the secondary pane"""
        half_change_size = amt / 2
        # track unshrinkable amounts
        left = amt
        # first secondary (top)
        if self.focused == 1:
            # only shrink downwards
            left -= amt - self.shrink_down_shared(0, amt)
        # last secondary (bottom)
        elif self.focused == len(self.clients) - 1:
            # only shrink upwards
            left -= amt - self.shrink_up(len(self.relative_sizes) - 1, amt)
        # middle secondary
        else:
            # get size index
            idx = self.focused - 1
            # shrink up and down
            left -= half_change_size - self.shrink_up_shared(idx, half_change_size)
            left -= half_change_size - self.shrink_down_shared(idx, half_change_size)
            left -= half_change_size - self.shrink_up_shared(idx, half_change_size)
            left -= half_change_size - self.shrink_down_shared(idx, half_change_size)
        # calculate how much shrinkage took place
        diff = amt - left
        # grow client by diff amount
        self.relative_sizes[self.focused - 1] += self._get_relative_size_from_absolute(diff)
Will grow the focused client in the secondary pane
libqtile/layout/xmonad.py