Lesson: Alternate Case of a Character in Python

Objective:

Learn how to alternate the case of a character in Python using two approaches: the old manual solution and the new bitwise solution.

Initial Code:

Here’s the starting code:

char = 'F'

for i in range(4):
    print(char)
    # Add one line here

The goal is to alternate the case of the character 'F' on each iteration, producing the following output:

F
f
F
f

Old Solution (Using ASCII Comparison)

The old solution manually checks the ASCII range of the character to toggle its case:

char = 'F'

for i in range(4):
    print(char)
    if 'A' <= char <= 'Z':  # Check if the character is uppercase
        char = chr(ord(char) + 32)  # Convert to lowercase by adding 32
    else:
        char = chr(ord(char) - 32)  # Convert to uppercase by subtracting 32

How It Works:

1. Check the Character Range:
   • 'A' <= char <= 'Z': Checks if the character is uppercase (ASCII range 65–90).
   • Else: Assumes the character is lowercase (ASCII range 97–122).
2. Toggle Case Using ASCII Arithmetic:
   • Uppercase → Lowercase:
     • Add 32 to the ASCII value (ord(char) + 32).
   • Lowercase → Uppercase:
     • Subtract 32 from the ASCII value (ord(char) - 32).
3. Convert Back to a Character:
   • chr() converts the updated ASCII value back to a character.

New Solution (Using Bitwise XOR)

The more efficient solution toggles the case using a bitwise operation:

char = 'F'

for i in range(4):
    print(char)
    char = chr(ord(char) ^ (1 << 5))

How It Works:

1. Convert the Character to ASCII:
   • ord(char) gets the ASCII value of the character.
2. Toggle the 5th Bit:
   • (1 << 5) creates a value of 32 (binary 00100000).
   • XOR (^) toggles the 5th bit of the ASCII value:
     • Uppercase → Lowercase
     • Lowercase → Uppercase
3. Convert Back to a Character:
   • chr() converts the modified ASCII value back to a character.

Output (Both Solutions):

F
f
F
f

Comparison of the Two Solutions:

Key Takeaways:

1. The old approach uses basic arithmetic and range checks, making it beginner-friendly.
2. The new bitwise approach is compact and efficient, ideal for optimizing performance.
3. Both solutions produce the same result but differ in style and complexity.