Regex in Python

Question

Does Python support recursion within regex?
Is it possible to check parentheses matching in a string just in one pattern, e.g. r"..." for an arbitrarily long "(())(()(("

Answer 1

Then I am afraid it won't be doable unless you somehow combine the lazy search for the exact "\(\)" matching, lazy for "\(*\)" and greedy for "\(*\)" and the last obe as a numbered or named group to match as many as possible.

Even then, though, there is a problem with "clean" (not disturbed) recurrent parenthesis, like (((())))

I can't seem to find a way for this case :/

Answer 2

There is a better module for this than re. It is called regex and seemingly it does support recursive search:
https://pypi.python.org/pypi/regex

Just use the ?R pattern.
However, using regex for this purpose is still not recommended - simple parsing would be quicker and more efficient.

Answer 3

Are you looking for a syntax matching or just a number of opening and closing beackets being equal?

Answer 4

by the way, here is the (recursive) code.
but I'm still looking for one line solution.
https://code.sololearn.com/cesSwXg4kmt6/?ref=app

Answer 5

But you can also do it iteratively :
def parenthesis(s):
count=0
i=0
while count>=0 and i<len(s):
if s[i]==')':
count-=1
elif s[i]=='(':
count+=1
i+=1
return count==0

Answer 6

I may be wrong but I think it is not a regular language that you are trying to check with regex, so it will not work :/

Answer 7

thanks, @Baptiste, I know the problem can be solved in a simple way, as you did. And my code is a mixture of re and code. again, I want to know whether it can be a line like re.findall(pattern, string) is True or False

Answer 8

That is what I answered in my first comment. You can define the input with good parenthesis as a language (a set of word of a finite/infinite size, in our case infinite). I will not go into the details but if you can prove it is a regular language, then it can be define by a regular expression (the reciprocate is also true). And I think it is not possible

Answer 9

syntax matching if possible