def _shrink(self, cidx, amt):
        """Reduce the size of a client

        Will only shrink the client until it reaches the configured minimum
        size. Any amount that was prevented in the resize is returned.
        """
        # get max resizable amount
        margin = self.get_shrink_margin(cidx)
        if amt > margin:  # too much
            self.relative_sizes[cidx] -= self._get_relative_size_from_absolute(margin)
            return amt - margin
        else:
            self.relative_sizes[cidx] -= self._get_relative_size_from_absolute(amt)
            return 0
Reduce the size of a client

        Will only shrink the client until it reaches the configured minimum
        size. Any amount that was prevented in the resize is returned.
        
libqtile/layout/xmonad.py