Firstly, I wrote something like this:

patn = r"\bROW\s*\((\d+|\*)\)(.|\s)*?\)"
    newlines = re.sub(patn, "\nYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY\n", newlines)
but if the file(or string) ended without the expected ")" the code deadlock there, no progress, no exception, and no exit.

Then I changed it to :
 patn = r"\bROW\s*\((\d+|\*)\)(.|\s)*?(\)|$)"
    newlines = re.sub(patn, "\nYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY\n", newlines) to enforce the rule of  end of file. then everything ok.

I felt this is a but, coz RE should not die, it should exit if can't match.

it is Py3.5 on ubuntu. Thanks!

Sorry, forgot I have upgraded to 3.6.2, not 3.5

Sorry again, the sample code offered is issue of re.sub(), not findall() :o)))

You don't give the value of 'newlines', but the problem is probably catastrophic backtracking, not deadlock.

Min, you need to give a complete example other people can actually run for themselves.

Offhand, this part of the regexp

(.|\s)*

all by itself _can_ cause exponential-time behavior. You can run this for yourself:

>>> import re
>>> p = r"(.|\s)*K"
>>> re.search(p, " " * 10) # fast
>>> re.search(p, " " * 15) # fast
>>> re.search(p, " " * 20) # obviously takes a bit of time
>>> re.search(p, " " * 21) # very obviously takes time
>>> re.search(p, " " * 22) # over a second
>>> re.search(p, " " * 25) # about 10 seconds

Etc.

Closing as not-a-bug - not enough info to reproduce, but the regexp looked prone to exponential-time backtracking to both MRAB and me, and there's been no response to requests for more info.

components: + Regular Expressions

nosy: + ezio.melotti
messages: + msg322599
resolution: not a bug
stage: resolved