@staticmethod
def get_expr(expr, follow, nofollow):
    """Update @follow/@nofollow according to insteresting nodes
        Returns same expression (non modifier visitor).

        @expr: expression to handle
        @follow: set of nodes to follow
        @nofollow: set of nodes not to follow
        """
    if expr.is_id():
        follow.add(expr)
    elif expr.is_int():
        nofollow.add(expr)
    elif expr.is_mem():
        follow.add(expr)
    return expr
