Re: Flubbed it in the second interation through the string: range error... HOW?

MRAB <python@mrabarnett.plus.com> wrote or quoted:

Small mistake there. The original code converted to uppercase on even
indexes, whereas your code does it on odd ones.

  Here follows my humble effort.

import doctest

def alternate_uppercase( s ):
    """
    Alternates the case of alphabetic characters in a given string.

    Args:
        s (str): The input string.

    Returns:
        str: The string with alternating uppercase and lowercase letters.

    Examples:
        >>> alternate_uppercase( 'Python is awesome!' )
        'PyThOn Is AwEsOmE!'

        >>> alternate_uppercase( 'ab,c,,d,,,e,,,,f' )
        'Ab,C,,d,,,E,,,,f'

        >>> alternate_uppercase( '' )
        ''
    """
    result =[ None ]* len( s )
    letter_count = 0
    for char_pos, char in enumerate( s ):
        if char.isalpha():
            result[ char_pos ]=\
            ( char.lower if letter_count%2 else char.upper )()
            letter_count += 1
        else:
            result[ char_pos ]= char
    return ''.join( result )

doctest.testmod()