Python | Alternate cases in String

Difficulty Level : Basic
Last Updated : 29 Dec, 2019

The problem of case changes a string is quite common and has been discussed many times. Sometimes, we might have a problem like this in which we need to convert the odd character of string to upper case and even positioned characters to lowercase. Let’s discuss certain ways in which this can be performed.

Method #1 : Using upper() + lower() + loop
This task can be performed in brute force method in a way that we iterate through the string and convert odd elements to uppercase and even to lower case using upper() and lower() respectively.

# Python3 code to demonstrate working of
# Alternate cases in String
# Using upper() + lower() + loop
  
# initializing string 
test_str = "geeksforgeeks"
  
# printing original string 
print("The original string is : " + str(test_str))
  
# Using upper() + lower() + loop
# Alternate cases in String
res = ""
for idx in range(len(test_str)):
    if not idx % 2 :
       res = res + test_str[idx].upper()
    else:
       res = res + test_str[idx].lower()
  
# printing result 
print("The alterate case string is : " + str(res))

Output :

The original string is : geeksforgeeks
The alterate case string is : GeEkSfOrGeEkS

Method #2 : Using list comprehension
This is the shortened one liner approach to this problem. It uses same logic as above but in much more compact way.

# Python3 code to demonstrate working of
# Alternate cases in String
# Using list comprehension
  
# initializing string 
test_str = "geeksforgeeks"
  
# printing original string 
print("The original string is : " + str(test_str))
  
# Using list comprehension
# Alternate cases in String
res = [ele.upper() if not idx % 2 else ele.lower() for idx, ele in enumerate(test_str)]
res = "".join(res)
  
# printing result 
print("The alterate case string is : " + str(res))

Output :

The original string is : geeksforgeeks
The alterate case string is : GeEkSfOrGeEkS

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