Compute sum of digits

Compute sum of digits of a given string.

def sum_digits_string(S):

    sum_digit = 0

    for chr in S:
        if chr.isdigit() == True:
            sum_digit += int(chr)

    return sum_digit

# test
print(sum_digits_string("123abcd45"))    # 15
print(sum_digits_string("abcd1234"))     # 10

See also

https://www.w3resource.com/python-exercises/string/python-data-type-string-exercise-62.php