Python - Reverse String except punctuations

Python – Reverse String except punctuations

Last Updated : 05 Sep, 2020

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 substing 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 alphabets

Python3

# Python3 code to demonstrate working of  
# Reverse String except punctuations 
# Using groupby() + isalnum() [ for substing 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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