怎么用python re模块匹配问号？

现在我用

 re.sub("?", "", some_string)

然后报错

 Traceback (most recent call last):
  File "insert_mysql.py", line 338, in <module>
    main()
  File "insert_mysql.py", line 255, in main
    f_1 = re.sub("?", "", f_0)
  File "/usr/lib/python2.7/re.py", line 155, in sub
    return _compile(pattern, flags).sub(repl, string, count)
  File "/usr/lib/python2.7/re.py", line 251, in _compile
    raise error, v # invalid expression
sre_constants.error: nothing to repeat

不知道怎么解决了，大神们快出手~

然后加了原生符

 re.sub(r"?", "", some_string)

还是不行

 问号需要转义，用\?

仅供参考

 '''针对字符串去除标点符号,[\s+\.\!\/_,$%^*(+\"\']+|'''
def SubPunctuation(str):
    s = re.sub(u"[+——！，。？、~@#￥%……&*（）：:¶]+", u"",str)
    return s