python - Python 正则表达式中允许的最大重复次数是多少？

Question

在 Python 2.7 和 3 中，以下工作:

>>> re.search(r"a{1,9999}", 'aaa')
<_sre.SRE_Match object at 0x1f5d100>

但这给出了一个错误:

>>> re.search(r"a{1,99999}", 'aaa')
 Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "/usr/lib/python2.7/re.py", line 142, in search
   return _compile(pattern, flags).search(string)
   File "/usr/lib/python2.7/re.py", line 240, in _compile
   p = sre_compile.compile(pattern, flags)
   File "/usr/lib/python2.7/sre_compile.py", line 523, in compile
   groupindex, indexgroup
RuntimeError: invalid SRE code

好像有重复次数的上限。这是正则表达式规范的一部分，还是特定于 Python 的限制？如果特定于 Python，是否在某处记录了实际数字，它是否因实现而异？

Answer 1

快速手动二进制搜索揭示了答案，特别是 65535:

>>> re.search(r"a{1,65535}", 'aaa')
<_sre.SRE_Match object at 0x2a9a68>
>>> 
>>> re.search(r"a{1,65536}", 'aaa')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/7.3/lib/python2.7/re.py", line 142, in search
    return _compile(pattern, flags).search(string)
  File "/Library/Frameworks/Python.framework/Versions/7.3/lib/python2.7/re.py", line 240, in _compile
    p = sre_compile.compile(pattern, flags)
  File "/Library/Frameworks/Python.framework/Versions/7.3/lib/python2.7/sre_compile.py", line 523, in compile
    groupindex, indexgroup
OverflowError: regular expression code size limit exceeded

这是讨论 here :

The limit is an implementation detail. The pattern is compiled into codes which are then interpreted, and it just happens that the codes are (usually) 16 bits, giving a range of 0..65535, but it uses 65535 to represent no limit and doesn't warn if you actually write 65535.

和

The quantifiers use 65535 to represent no upper limit, so ".{0,65535}" is equivalent to ".*".

---

感谢以下评论的作者指出了更多内容:

• CPython 在 _sre.c 中实现了这个限制. (@LukasGraf)

• sre_constants.py 中有一个常量MAXREPEAT拥有这个最大重复值:

  >>> import sre_constants
  >>> 
  >>> sre_constants.MAXREPEAT
  65535
  

  (@MarkkuK。和@hcwhsa)