Python Program for Convert characters of a string to opposite case

In this problem, we will toggle the case of each string character. The easiest way to toggle the case of each string character is using the swapcase() built-in method.

Also, we can use the ASCII values of the characters to swap their case. Python also contains isupper() and islower() methods to check the character's case and the lower() and upper() methods to change the case.

Problem statement We have given a string. We need to toggle the case of string characters. It means converting uppercase characters to lowercase and lowercase characters to uppercase.

Sample Examples

Input

alpha = "TutorialsPoint"

Output

'tUTORIALSpOINT'

Explanation Here, we have toggled the case of each character.

Input

alpha = '12qwER@'

Output

'12QWer@'

Explanation We changed the case of each alphabetical character and kept special characters as they are.

Using ASCII Values

In this approach, we add 32 to the ASCII value if the character is uppercase. Otherwise, we subtract 32 from the ASCII value to convert it to uppercase ?

Algorithm

Step 1 Convert the string to a list of characters.

Step 2 Traverse the list of characters.

Step 3 If the character is between 'A' to 'Z', add 32 to the ASCII value.

Step 4 If the character is between 'a' to 'z', subtract 32 from the ASCII value.

Step 5 Use the join() method to convert the list back to a string.

Example

def changeCase(alpha):
    alpha_list = list(alpha)  # String to list
    
    # Traverse list of string characters
    for p in range(len(alpha_list)):
        if alpha_list[p] >= 'A' and alpha_list[p] <= 'Z':
            alpha_list[p] = chr(ord(alpha_list[p]) + 32)  # Change to lowercase
        elif alpha_list[p] >= 'a' and alpha_list[p] <= 'z':
            alpha_list[p] = chr(ord(alpha_list[p]) - 32)  # Change to uppercase
    
    alpha = ''.join(alpha_list)  # List to string
    return alpha

alpha = "TutorialsPoint"
result = changeCase(alpha)
print("The string after flipping the case of each character is -", result)

The string after flipping the case of each character is - tUTORIALSpOINT

Time complexity O(N) to traverse the string characters.

Space complexity O(N) to store the string in the list of characters.

Using isupper() and Case Methods

In this approach, we use the isupper() method to check whether the character is uppercase. We use the upper() and lower() methods to convert the character accordingly ?

Example

def changeCase(alpha):
    temp = ""
    for ch in alpha:
        # Using the isupper() method to check if character is uppercase
        if ch.isupper():
            # Converting character to lowercase
            temp += ch.lower()
        else:
            temp += ch.upper()  # Converting character to uppercase
    return temp

alpha = "TutorialsPoint"
result = changeCase(alpha)
print("The string after flipping the case of each character is -", result)

The string after flipping the case of each character is - tUTORIALSpOINT

Time complexity O(N) for traversing the string.

Space complexity O(N) to store the resultant string.

Using swapcase() Method

The swapcase() method is the built-in Python method that directly toggles the case of all characters in a string ?

Example

def changeCase(alpha):
    # Using the swapcase() function to toggle the case of characters
    return alpha.swapcase()

alpha = "AbcSDe"
result = changeCase(alpha)
print("The string after flipping the case of each character is -", result)

The string after flipping the case of each character is - aBCsdE

Time complexity O(N)

Space complexity O(1)

Using Regular Expression

In this approach, we use regular expressions and lambda functions to toggle the case of each string character ?

Example

import re

def changeCase(alpha):
    # Regular expression pattern to match alphabetical characters
    patt = r'[a-zA-Z]'
    
    # Toggle case of each character using lambda function
    alpha = re.sub(patt, lambda ch: ch.group().lower()
                   if ch.group().isupper() else ch.group().upper(), alpha)
    return alpha

alpha = "TutorialsPoint"
result = changeCase(alpha)
print("The string after flipping the case of each character is -", result)

The string after flipping the case of each character is - tUTORIALSpOINT

Time complexity O(N)

Space complexity O(1)

Using XOR Operation

In this approach, we perform the XOR operation of the ASCII value with 32 to toggle the case. When we XOR 32 with any alphabetical character, it toggles the 6th bit of the binary representation ?

For example:

• 65 = 'A' = 1000001

• 97 = 'a' = 1100001

• 32 = 0100000

When we XOR 65 and 32, it becomes 97 as the 6th bit gets flipped.

Example

def isAlphabeticChar(char):
    ascii_val = ord(char)
    # Using ASCII values to validate character
    if (ascii_val >= 65 and ascii_val <= 90) or (ascii_val >= 97 and ascii_val <= 122):
        return True
    else:
        return False

def changeCase(alpha):
    temp = ""
    for ch in alpha:
        if isAlphabeticChar(ch):
            temp += chr(ord(ch) ^ (1 << 5))  # XOR with 32 (which is 1<<5)
        else:
            temp += ch
    return temp

alpha = "TutorialsPoint"
result = changeCase(alpha)
print("The string after flipping the case of each character is -", result)

The string after flipping the case of each character is - tUTORIALSpOINT

Time complexity O(N)

Space complexity O(N)

Comparison

Conclusion

The swapcase() method is the most efficient and readable approach for toggling character case. For learning purposes, the ASCII manipulation and XOR approaches help understand low-level string operations.