How to search a string with parentheses using regular expression?

Question

I have a txt file containing strings as:

   A 123
   B  456
   Ab(123)
   ......

I wish to search Ab(123) in txt file.

What I have tried :

re.search(r'Ab(123)',string)

Answer 1

There are 12 characters with special meanings, you escape to its literal meaning with \ in front of it.

re.search(r'Ab\(123\)',string)

# or re.findall(r'Ab\(123\)',string)

Look up https://regex101.com/r/1bb8oz/1 for detail.

Answer 2

Ab\(123\)

In regex, there are 12 characters with special meanings: the backslash \, the caret ^, the dollar sign $, the period or dot ., the vertical bar or pipe symbol |, the question mark ?, the asterisk or star *, the plus sign +, the opening parenthesis (, the closing parenthesis ), the opening square bracket [, and the opening curly brace {, these special characters are often called metacharacters and should be escaped with backslash Ab\(123\) if used as literal.
This can be automagically achieved using re.escape()

import re
string = "some text Ab(123) and more text"
if re.search(re.escape("Ab(123)"),string):
  print("match")

---

• Regex Special Characters
• Python Demo

Answer 3

Do you really need regex in the first place, if your goal is just to extract the lines where you have parentheses.

You could use the following approach:

input:

$ cat parentheses.txt 
A 123
B  456
Ab(123)
uV(a5afgsg3)
A 123

output:

$ python parentheses.py 
['Ab(123)', 'uV(a5afgsg3)']

code:

with open('parentheses.txt') as f:
    content = f.readlines()
content = [x.strip() for x in content if '(' in x and ')' in x]
print(content)

If you really want to use regex:

import re

s = """
A 123
B  456
Ab(123)
uV(a5afgsg3)
A 123
"""
print(re.findall(r'^.*?\(.*?\).*$',s,re.MULTILINE))

output:

['Ab(123)', 'uV(a5afgsg3)']

demo: https://regex101.com/r/PGsguA/1