Extract string between two brackets, including nested brackets in python

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How to extract string between two brackets, including the nested brackets.

There is a string:

""res = sqr(if((a>b)&(a<c),(a+b)*c,(a-b)*c)+if()+if()...)""

How can I extract the all the contents of if() as following:

["if((a>b)&(a<c),(a+b)*c,(a-b)*c)","if()","if()",...]

The format is not fixed, the string may includes multi-ifs. So I want to know if there is a pattern that can match the substring. I'll try to give my solution later. thanks.

My solution, if there is any better method, please point out to me:

def extractIfFunc(condStr):

startIndex = [m.start() for m in re.finditer('if\(',condStr)]
parts = []
for index in startIndex:
    current = []
    bracket_level = 0
    for s in condStr[index+3:]:
        if s != '(' and s != ')' and bracket_level >= 0:
            current.append(s)
        elif s == '(':
            current.append(s)
            bracket_level += 1
        elif s == ')':
            bracket_level -= 1 
            if bracket_level < 0:
                current.append(s)
                break
            else:
                current.append(s)     
    parts.append('if('+''.join(current))
return parts  
>>> import re
>>> s = """res = sqr(if((a>b)&(a<c),(a+b)*c,(a-b)*c)+if()+if()...)"""
>>> re.findall(r'if\((?:[^()]*|\([^()]*\))*\)', s)
['if((a>b)&(a<c),(a+b)*c,(a-b)*c)', 'if()', 'if()']

For such patterns, better to use VERBOSE flag:

>>> lvl2 = re.compile('''
...          if\(            #literal if(
...            (?:           #start of non-capturing group
...             [^()]*       #non-parentheses characters
...             |            #OR
...             \([^()]*\)   #non-nested pair of parentheses
...            )*            #end of non-capturing group, 0 or more times
...          \)              #literal )
...          ''', flags=re.X)
>>> re.findall(lvl2, s)
['if((a>b)&(a<c),(a+b)*c,(a-b)*c)', 'if()', 'if()']

To match any number of nested pairs, you can use regex module, see Recursive Regular Expressions

Extract string inside nested brackets, x here is your string holding value which is (text) , to extract only text without the John Connor, I've used Python 2 and 3, and Iron Python in Visual Studio expressions in Python to match the brackets and extract the text between them. this should work with any string holding any letters before or after the brackets like  Note, the string could have N brackets, and they will always be valid, but may or may not be nested. Also, the string doesn't have to start with a bracket. The solutions I have found online to a similar problem suggest a regex, but I'm not sure it will work in this case.

Try This:

st[st.find('(')+1:st.rfind(')')]

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st = """res = sqr(if((a>b)&(a<c),(a+b)*c,(a-b)*c))"""

print(st[10:][:-1])

OUTPUT:

if((a>b)&(a<c),(a+b)*c,(a-b)*c)

EDIT:

For a generic approach:

import re
st = """res = sqr(if((a>b)&(a<c),(a+b)*c,(a-b)*c))"""
pattern = "\((.*)\)"
print(re.compile(pattern).search(st).group(1))

Where:

\( matches the character ( literally (case sensitive)

1st Capturing Group (.*)

.* matches any character (except for line terminators)

\) matches the character ) literally

OUTPUT:

if((a>b)&(a<c),(a+b)*c,(a-b)*c)

regexTester

How to extract substrings between brackets while ignoring those , Regex to grab strings between square brackets, You are almost there, you just need a ie. sample some another one Note: In my use case, brackets cannot be nested. [Solved] Get a text inside square brackets with regex ( regular , You're only looking for a 3.9K views Extract text between two square brackets in python. Let's say I have a string 'gfgfdAAA1234ZZZuijjk' and I want to extract just the '1234' part.. I only know what will be the few characters directly before AAA, and after ZZZ the part I am interested in 1234.

def extractIfFunc(condStr):
    for i, segment in enumerate(a.split("if")):
        if i == 0:
            continue

        s, n = -1, 0
        for i, c in enumerate(segment):
            if c == '(':
                s = i if s < 0 else s
                n += 1
            elif c == ')':
                n = n - 1 if n > 0 else 0
                if n == 0 and s > -1:
                    yield "if(%s)" % segment[s + 1:i]
                    break


a = """res = sqr(if((a>b)&(a<c),(a+b)*c,(a-b)*c)+if()+if()...)"""

for segment in extractIfFunc(a):
    print(segment)

NOTE:

This is not a real parser. If you want to create a parser that matches LALR(1) grammar, maybe the PLY is what you are looking for. It can help you to build a complete parser.

Regular expression to extract text between square brackets, A regular expression is a pattern that is matched against a string from left to right. The power of regular expressions comes from the ability to include Part of a pattern that is in square brackets is called a "character class". between \x{ and }​, but the value of the character code must be less than 2**31 as in Python. If I have a string such as: "You id is (1) and your number is (0000000000)" What is the best way to extract these these strings into a list of strings. The numbers between the brackets can increase in digits thus searching for the strings between the brackets is a better technique. I can use the code below to extract the first string between

Regular expression syntax, Lists are enclosed in square brackets ( [ and ] ) and tuples in parentheses ( ( and ) ). A list containing no elements is called an empty list, and a tuple with no if you imagine the indices pointing between the characters, as in the following diagram: To extract an element from the nested list, we can proceed in two steps:. 2.1.2. Physical lines¶. A physical line is a sequence of characters terminated by an end-of-line sequence. In source files and strings, any of the standard platform line termination sequences can be used - the Unix form using ASCII LF (linefeed), the Windows form using the ASCII sequence CR LF (return followed by linefeed), or the old Macintosh form using the ASCII CR (return) character.

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3. Strings, lists, and tuples, Python: How to match nested parentheses with regex?, The regular I need a regular expression to select all the text between two outer brackets. javascript, I​'m trying to remove parentheses from a string using regex, can I get some We can​  A Python program can read a text file using the built-in open() function. For example, the Python 3 program below opens lorem.txt for reading in text mode, reads the contents into a string variable named contents, closes the file, and prints the data.

Comments
  • If all your inputs are in the form "varname = funcname(expression)", then it's quite easy - just find the position of the first opening paren and you're basically done. Now if you want to be able to parse arbitrary expressions / statements, you'll need a proper parser for this language, whatever it is.
  • tomassetti.me/parsing-in-python
  • @brunodesthuilliers, yes, that's what i exactly want to do.
  • @Jimmy "yes, that's what i exactly want to do" => what ?
  • what about ""result = sqrt(if((a>b)&(a<c),(a+b)*c,(a-b)*c))"" ? This is not a global answer!
  • It looked like a fixed string manipulation, however I will edit and add a global approach after lunch, cheers
  • Enjoy your meal :)