def METHOD_NAME(hypo_depth_dist, use_default=False):
    """
    Returns the hypocentral depth distribtuion as an instance of the :class:
    openquake.hazardlib.pmf. 
    """
    if isinstance(hypo_depth_dist, PMF):
        # Is already instance of PMF
        return hypo_depth_dist
    else:
        if use_default:
            # Default value of 10 km accepted
            return PMF([(1.0, 10.0)])
        else:
            # Out of options - raise error!
            raise ValueError('Hypocentral depth distribution not defined!')