def _build_regex_range(ws=True, invert=False, exclude=None):
    if exclude is None:
        exclude = []
    regex = ""
    # are we currently in a range
    in_range = False
    # last character we found, for closing ranges
    last = None
    # last character we added to the regex, this lets us know that we
    # already have B in the range, which means we don't need to close
    # it out with B-B. While the later seems to work, it's kind of bad form.
    last_added = None

    def valid_char(char):
        if char in exclude:
            result = False
        elif ws:
            result = _is_printable(char)
        else:
            # Zs is the unicode class for space characters, of which
            # there are about 10 in this range.
            result = (_is_printable(char) and
                      unicodedata.category(char) != "Zs")
        if invert is True:
            return not result
        return result

    # iterate through the entire character range. in_
    for c in _get_all_chars():
        if valid_char(c):
            if not in_range:
                regex += re.escape(c)
                last_added = c
            in_range = True
        else:
            if in_range and last != last_added:
                regex += "-" + re.escape(last)
            in_range = False
        last = c
    else:
        if in_range:
            regex += "-" + re.escape(c)
    return regex
Build a range regex for a set of characters in utf8.
dataset/ETHPy150Open BU-NU-CLOUD-SP16/Trusted-Platform-Module-nova/nova/api/validation/parameter_types.py/_build_regex_range