An implementation of string equality comparison case-insensitive e.g. s1.upper() == s2.upper()

case_insinsitive_compare.py

def case_insensitive(s1, s2):
    """
    returns True if both s1 and s2 
    contain the same letters and letters in the same order,
    regardless of letters case.
    In other words, 
    this is an implementation for either 
        s1.upper() == s2.upper() 
    or  s1.lower() == s2.lower()
    """

    def alpha_range(ord_val):
        upper_vals = range(65, 91)  # unicode code values of A - Z
        lower_vals = range(97, 123) # unicode code values of a - z
        valid_values = tuple(list(upper_vals) + list(lower_vals))
        return ord_val in valid_values

    if len(s1) != len(s2):
        return False
    
    for c1, c2 in zip(s1, s2):
        # diff in Unicode code value
        diff = abs(ord(c1) - ord(c2))
        
        not_upper_lower_distance = diff != 32
        not_same_letter_distance = diff != 0
        not_same_distance = not_upper_lower_distance and not_same_letter_distance
        if not_same_distance:
            return False
        
        # make sure that not any difference of 32 can pass
        # e.g. diff between ord('?') and ord('_')
        within_alphabet_range = alpha_range(ord(c1)) and alpha_range(ord(c2))
        if not within_alphabet_range:
            return False
    return True


print(case_insensitive('abc', 'AbC'))  # True
print(case_insensitive('bbC', 'Bbc'))  # True
print(case_insensitive('ac c', 'aC'))  # False
print(case_insensitive('aca', 'acå'))  # False