CODEWITHSUNDEEP
pythonregexpython-3.x
Mridula Gunturi
Mridula Gunturi

Reputation: 187

Find text contained within outermost parentheses in a math expression

I am trying to find text contained within the outermost brackets of a function, filt().

The function is part of a math expression string:

math_expr = "filt(2*A) + filt(A*(B+C)) - filt((A+B)/(C+D))"

The expected output is:

['2*A', 'A*(B+C)', '(A+B)/(C+D)']

I have tried using several regex expressions on this site, the closest output I got was by using re.findall('\((.*?)\)', math_expr). However, the regex returns:

['2*A', 'A*(B+C', '(A+B', 'C+D']

Could someone please help me? I am new to regex and don't know what else to try. Thank you!

Upvotes: 1

Views: 670

Answers (3)

FailSafe
FailSafe

Reputation: 482

Just as a really easy alternative

>>> import re

>>> math_expr = "filt(2*A) + filt(A*(B+C)) - filt((A+B)/(C+D))"

>>> re.findall(r'\(([\S]*?)\)(?=\s|$)', math_expr)


#OUTPUT
['2*A', 'A*(B+C)', '(A+B)/(C+D)']

Upvotes: 1

Albin Paul
Albin Paul

Reputation: 3419

I have coded it up using a stack approach. It just puts in ( into a stack and then pops from it when you see a ).

math_expr = "filt(2*A) + filt(A*(B+C)) - filt((A+B)/(C+D))"
stack = []
index = 0
overallresult = []
while (index < len(math_expr)):
    if math_expr[index] == '(':
        stack.append('(')
        result = ''
        index +=1
        while(index<len(math_expr) and len(stack)>0):
            result += math_expr[index]
            if(math_expr[index]=='('):
                stack.append('(')
            elif (math_expr[index]==')'):
                stack.pop()
            index+=1
        overallresult.append(result[:-1])
    index+=1
print(overallresult)

OUTPUT

['2*A', 'A*(B+C)', '(A+B)/(C+D)']

Upvotes: 0

CertainPerformance
CertainPerformance

Reputation: 370689

If you use the regex module, which supports recursive patterns, you can use

regex.findall(r'\(((?:[^()]+|(?R))+)\)', math_expr)

Output:

['2*A', 'A*(B+C)', '(A+B)/(C+D)']

https://regex101.com/r/oclWxx/1

  • \( - Leading parentheses
  • ((?:[^()]+|(?R))+) - Capturing group, which repeatedly matches:
    • [^()]+ - Anything but parentheses, or
    • (?R) - The entire pattern, recursed again
  • \) - Trailing parentheses

Upvotes: 2

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