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Python Program to reverses alternate strings and then concatenates all elements
  • Last Updated : 22 Oct, 2020
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Given a String List, the following program returns a concatenated list of all its string elements with its alternate elements reversed.

Input : test_str = ‘geeksgeeks best for geeks’ 
Output : skeegskeeg best rof geeks 
Explanation : Alternate words reversed.
Input : test_str = ‘geeksgeeks best geeks’ 
Output : skeegskeeg best skeeg 
Explanation : Alternate words reversed. 

Method 1 : Using reversed() and loop

In this, we perform the task of reversing strings using reversed() and then check for alternates using % operator and concatenate accordingly.

Python3




# initializing string
test_str = 'geeksgeeks is best for geeks' 
  
# printing original string
print("The original string is : " + str(test_str))
  
# spliting string 
temp = test_str.split()
  
res = []
for idx in range(len(temp)):
      
    # reversing if alternate
    if idx % 2 == 0:
        res.append(''.join(list(reversed(temp[idx]))))
    else :
        res.append(temp[idx])
          
res = ' '.join(res)
  
# printing result 
print("Transformed String : " + str(res)) 

Output:



The original string is : geeksgeeks is best for geeks

Transformed String : skeegskeeg is tseb for skeeg

Method 2 : Using slicing and list comprehension

In this, we perform task fo reversal using slicing and then list comprehension is used to perform the task done by loop, in shorthand.

Python3




# initializing string
test_str = 'geeksgeeks is best for geeks' 
  
# printing original string
print("The original string is : " + str(test_str))
  
# spliting string 
temp = test_str.split()
  
# list comprehension to solve problem in 1 liner
res = ' '.join([''.join(list(reversed(temp[idx]))) if idx % 2 == 0 else temp[idx] for idx in range(len(temp))])
  
# printing result 
print("Transformed String : " + str(res)) 

Output:

The original string is : geeksgeeks is best for geeks

Transformed String : skeegskeeg is tseb for skeeg

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