'Finds digits in a string and returns a list with string sections.
>>> ds = digit_sum()
>>> ds._find_digits(\'foo45\')
[\'foo\', \'45\']
>>> ds._find_digits(\'f001bar112\')
[\'f\', \'001\', \'bar\', \'112\']
:return: A list of strings.'

def _find_digits(self, a_string):

    return [x for x in DIGIT_REGEX.split(a_string) if (x != '')]
