Python – Reverse String except punctuations

Last Updated : 15 Jul, 2021

Given a string with punctuations, perform string reverse, leaving punctuations at their places.

Input : test_str = ‘geeks@#for&%%gee)ks’
Output : skeeg@#rof&%%ske)eg
Explanation : Whole string is reveresed, except the punctuations.
Input : test_str = ‘geeks@#for&%%gee)ks’ [ only substring reversal ]
Output : skeeg@#rof&%%eeg)sk
Explanation : Only substrings are reversed.

Method #1 : Using loop + stack + punctuation + split()

In this, we use stack to perform string reversal, checking for punctuation, if current character is one, we append that. The split method is used to handle cases of spaces, which needs to be ignored while reverse.

Python3

# Python3 code to demonstrate working of
# Reverse String except punctuations
# Using loop + stack + punctuation + split()
from string import punctuation
 
# initializing string
test_str = 'geeks# for&%% gee)ks'
 
# printing original string
print("The original string is : " + str(test_str))
 
# getting punctuations
punc_set = set(punctuation)
res = []
for sub in test_str.split(' '):
     
    # getting all aphabets
    alphas = [chr for chr in sub if chr not in punc_set]
    for chr in sub:
         
        # checking for punctuations
        if chr not in punc_set:
            res.append(alphas.pop())
            continue
        else:
            res.append(chr)
             
    # handling spaces
    res.append(' ')
res = "".join(res)
 
# printing result
print("The Reversed String ignoring punctuation : " + str(res))

Output

The original string is : geeks#for&%%gee)ks
The Reversed String ignoring punctuation : skeeg#rof&%%ske)eg

Method #2 : Using groupby() + isalnum() [ for substring specific reversal ]

In this, we form grouping of each of substring between punctuations and reverse them among them, not whole. The isalnum() is used to check for all the alphabets.

Python3

# Python3 code to demonstrate working of
# Reverse String except punctuations
# Using groupby() + isalnum() [ for substring specific reversal ]
from itertools import groupby
 
# initializing string
test_str = 'geeks# for&%% gee)ks'
 
# printing original string
print("The original string is : " + str(test_str))
 
res = ''
 
# grouping all sections
for ele, sub in groupby(test_str, str.isalnum):
    sub = list(sub)
     
    # reversal on alphanumeric occurrence
    if ele:
        sub = sub[::-1]
         
    # joining all subparts
    res += ''.join(sub)
 
 
# printing result
print("The Reversed String ignoring punctuation [substring] : " + str(res))

Output

The original string is : geeks#for&%%gee)ks
The Reversed String ignoring punctuation [substring] : skeeg#rof&%%eeg)sk

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