def multi_find(source, target, start, end):
    '''Finds all occurrences of the substring target in the
       string source, within the range start <= pos < end.
       Returns a comma-separated string of values.'''

    result = ''
    pos = start

    while pos < end:
        next_pos = source.find(target, pos, end)

        if next_pos == -1:
            break
        result += (str(next_pos) + ',')
        pos = next_pos + 1

    if result == '':
        return result
    return result[:-1]