Basic Python - Extracting Strings

Question

I am trying to extract what's between parenthesis (including parenthesis) recursively.

This is my solution:

def paren(txt):
  if txt[1] == ")":
    return ''
  if txt[0] == "(":
    if len(txt) > 2:
        return txt[1]  + paren(txt[:1] + txt[2:])
    return txt[1]
  if len(txt) > 2:
    return paren(txt[1:])
  return ""

But it doesn't include any parenthesis. How can I fix it?

Example:

print paren("h(ello)o")
Output: (ello)
print paren("(hello)")
Output: (hello)

So are you trying to find the text inside the innermost set of parentheses? — JPeroutek, Jul 29 '15 at 15:16
Can you give an example before and after of what you want this to do? — Rich Sala, Jul 29 '15 at 15:18
Will there only be one set of parenthesis? What should happen here: `'(h(ello))'`? — kylieCatt, Jul 29 '15 at 15:28
possible duplicate of [Regular expression to return text between parenthesis](http://stackoverflow.com/questions/4894069/regular-expression-to-return-text-between-parenthesis) — kylieCatt, Jul 29 '15 at 15:30
@Zee please update your question. Also what do you mean by saying 'extract what's between parenthesis recursively`? If there is only one set of parenthesis then I do not understand why you want to do it recursively — Konstantin, Jul 29 '15 at 15:30
@Zee assuming there is only one pair of parenthesis check my solution — Halcyon Abraham Ramirez, Jul 29 '15 at 15:33

score 2 · Answer 1 · edited May 23 '17 at 12:30

If you have a single pair of parenthesis, I would recommend to go with Halcyon Abraham Ramirez's answer. Otherwise, try this method:

def paren(text):
    pstack = 0
    start = 0
    end = len(text)
    for i, c in enumerate(text):
        if c == '(':
            if pstack == 0:
                start = i
            pstack += 1
        elif c == ')':
            pstack -= 1
            if pstack == 0:
                end = i
                break

    return text[start:end]

And here is an example:

>>> paren("h(ello)")
'(ello)'

If you do not need the root parenthesis, you can modify the return statement like this:

return text[start+1:end-1]

And again:

>>> paren("h(ello)")
'ello'

Halcyon Abraham Ramirez · Answer 2 · 2015-08-26T18:52:29.830

2

use index

word = "hehlllllllll(ooooo)jejejeje"

def extract(word):
    return word[word.index("("):word.index(")") + 1]

output:

(ooooo)

taking it further. if there are multiple parenthesis:

a = "h((el(l))o"

def extract_multiple_parenthesis(word):
    closing_parenthesis = word[::-1].index(")")
    last_parenthesis_index = (len(word) - closing_parenthesis)
    return  word[word.index("("):last_parenthesis_index]

output:

((el(l))

edited Aug 26 '15 at 18:52

answered Jul 29 '15 at 15:26

Halcyon Abraham Ramirez

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@n9code op mentioned about having only one set of parenthesis. so this solution should suffice – Halcyon Abraham Ramirez Jul 29 '15 at 15:42
1

already removed my comment :) just noticed [OP's comment](http://stackoverflow.com/questions/31704502/basic-python-extracting-strings/31704715#comment51348150_31704502) – bagrat Jul 29 '15 at 15:42
@n9code it's all cool :D – Halcyon Abraham Ramirez Jul 29 '15 at 15:45

Basic Python - Extracting Strings

2 Answers2