def hstr(self, places=2, warn=True):
        """Convert to a string like ``12h 07m 30.00s``."""
        if warn and self.preference != 'hours':
            raise WrongUnitError('hstr')
        if self.radians.size == 0:
            return '<Angle []>'
        hours = self._hours
        shape = getattr(hours, 'shape', ())
        if shape and shape != (1,):
            return "{0} values from {1} to {2}".format(
                len(hours),
                _hstr(min(hours), places),
                _hstr(max(hours), places),
                )
        return _hstr(hours, places)
Convert to a string like ``12h 07m 30.00s``.