<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def addextension(path, ext=None):
 """ Helper function for handling of paths given separately passed file extensions. """

    if ext:
        if '*' in path:
            return path
        elif os.path.splitext(path)[1]:
            return path
        else:
            if not ext.startswith('.'):
                ext = '.'+ext
            if not path.endswith(ext):
                if not path.endswith(os.path.sep):
                    path += os.path.sep
                return path + '*' + ext
            else:
                return path
    else:
        return path