def _get_codepage_char_map(self, encoding):
        """ Get codepage character map

        Process an encoding and return a map of UTF-characters to code points
        in this encoding.

        This is generated once only, and returned from a cache.

        :param encoding: The name of the encoding.
        """
        # Skip things that were loaded previously
        if encoding in self.available_characters:
            return self.available_characters[encoding]
        codepage_char_list = self._get_codepage_char_list(encoding)
        codepage_char_map = dict((utf8, i + 128) for (i, utf8) in enumerate(codepage_char_list))
        self.available_characters[encoding] = codepage_char_map
        return codepage_char_map
Get codepage character map

        Process an encoding and return a map of UTF-characters to code points
        in this encoding.

        This is generated once only, and returned from a cache.

        :param encoding: The name of the encoding.