def physical_pin(self, function):
        """
        Return the physical pin supporting the specified *function*. If no pins
        support the desired *function*, this function raises :exc:`PinNoPins`.
        If multiple pins support the desired *function*, :exc:`PinMultiplePins`
        will be raised (use :func:`physical_pins` if you expect multiple pins
        in the result, such as for electrical ground).

        :param str function:
            The pin function you wish to search for. Usually this is something
            like "GPIO9" for Broadcom GPIO pin 9.
        """
        result = self.physical_pins(function)
        if len(result) > 1:
            raise PinMultiplePins('multiple pins can be used for %s' % function)
        elif result:
            return result.pop()
        else:
            raise PinNoPins('no pins can be used for %s' % function)