def coerce(cls, string):
        """Create a :class:`Requirement` object from a given package spec."""
        match = re.match(cls.spec_regex, string)
        if not match:
            raise InvalidRequirementSpecError("could not parse requirement")
        package = match.group(1)
        if all(match.group(2, 3)):
            version = "".join(match.group(2, 3))
        else:
            version = None
        return cls(package, version)
def _getQUICHeader(self, count):
        if type(count) is not hex:
            try:
                count_id = chr(count)
            except:
                sys.stderr.write("Count must be int or hex.\n")
                return 1
        else:
            count_id = count

        if count > self.max_packets:
            sys.stderr.write("[-]\tCount must be maximum of 255.\n")
            return 1

        header = "\x0c"                     # Public Flags
        header += self.sequence             # Adding CID
        header += count_id                  # Packet Count
        return header