Return a individual object
        
            Args:
                ind_id (str): A individual id
            
            Returns:
                individual (puzzle.models.individual)

def individual(self, ind_id=None):
        """Return a individual object
        
            Args:
                ind_id (str): A individual id
            
            Returns:
                individual (puzzle.models.individual)
        """
        for ind_obj in self.individual_objs:
            if ind_obj.ind_id == ind_id:
                return ind_obj
        return None