判断语句中小括号是否正确

def p(s):
    n9 = s.count("(")
    n0 = s.count(")")
    if n9 == n0:
        nn = s.rfind("(")
        left = s[0:nn+1]
        right = s[nn+1:]
        if left.count("(") == right.count(")"):
            print "yes"
        else:
            print "no"
    else:
        print "no"
if __name__ == "__main__":
    str = "(((())))"
    p(str)
    str2 = "zx(4er(1(er(Yy)ol)ol)ik"
    p(str2)
    str3 = "zx(4er(1(er(Yy)o)l)ol)ik)"
    p(str3)