def strip_non_ascii(s):
    """
    Returns the string without non-ASCII characters.

    Parameters
    ----------
    string : string
        A string that may contain non-ASCII characters.

    Returns
    -------
    clean_string : string
        A string that does not contain non-ASCII characters.

    """
    stripped = (c for c in s if 0 < ord(c) < 127)
    clean_string = u''.join(stripped)
    return clean_string