Python/Regex: Split string if a line does contain a certain special character

Question

I'm trying to split a multiline string on a character but only if the line does not contain : . Unfortunately I can't see an easy way to use re.split() with negative lookback on the character : since it's possible that : occurred in another line earlier in the string.

As an example, I'd like to split the below string on ) .

String:

Hello1 (
First : (),
Second )

Hello2 (
First 
)

Output:

['Hello1 (\nFirst : (),\nSecond', 'Hello2 (\nFirst \n']

Answer 1

It is possible with Python , albeit not "out of the box" with the native re module.

First alternative

The newer regex module supports a variable-length lookbehind, so you could use

(?<=^[^:]+)\)
# pos. lookbehind making sure there's no : in that line

---

In Python :

 import regex as re data = """ Hello1 ( First : (), Second ) Hello2 ( First )""" pattern = re.compile(r'(?<=^[^:]+)\\)', re.MULTILINE) parts = pattern.split(data) print(parts) 

Which yields

 ['\\nHello1 (\\nFirst : (),\\nSecond ', '\\n\\nHello2 (\\nFirst \\n', ''] 

---

Second alternative

Alternatively, you could match the lines in question and let them fail with (*SKIP)(*FAIL) afterwards:

 ^[^:\\n]*:.*(*SKIP)(*FAIL)|\\) # match lines with at least one : in it # let them fail # or match ) 

---

Again in Python :

 pattern2 = re.compile(r'^[^:\\n]*:.*(*SKIP)(*FAIL)|\\)', re.MULTILINE) parts2 = pattern.split(data) print(parts2) 

See a demo for the latter on regex101.com .

---

Third alternative

Ok, now the answer is getting longer than previously thought. You can even do it with the native re module with the help of a function. Here, you need to substitute the ) in question first and split by the substitute:

 def replacer(match): if match.group(1) is not None: return "SUPERMAN" else: return match.group(0) pattern3 = re.compile(r'^[^:\\n]*:.*|(\\))', re.MULTILINE) data = pattern3.sub(replacer, data) parts3 = data.split("SUPERMAN") print(parts3)