@classmethod
def _follow_exprs(cls, exprs, follow_mem=False, follow_call=False):
    """Extracts subnodes from exprs and returns followed/non followed
        expressions according to @follow_mem/@follow_call

        """
    follow, nofollow = set(), set()
    for expr in exprs:
        expr.visit(lambda x: cls.get_expr(x, follow, nofollow), lambda x:
            cls.follow_expr(x, follow, nofollow, follow_mem, follow_call))
    return follow, nofollow
