Method _find_encoding_token

data_compression/lz77.py:144–181

Finds the encoding token for the first character in the text. Tests: >>> lz77_compressor = LZ77Compressor() >>> lz77_compressor._find_encoding_token("abrarrarrad", "abracad").offset 7 >>> lz77_compressor._find_encoding_token("adabrarrarrad", "

(self, text: str, search_buffer: str)

        return output

    def _find_encoding_token(self, text: str, search_buffer: str) -> Token:
        """Finds the encoding token for the first character in the text.

        Tests:
            >>> lz77_compressor = LZ77Compressor()
            >>> lz77_compressor._find_encoding_token("abrarrarrad", "abracad").offset
            7
            >>> lz77_compressor._find_encoding_token("adabrarrarrad", "cabrac").length
            1
            >>> lz77_compressor._find_encoding_token("abc", "xyz").offset
            0
            >>> lz77_compressor._find_encoding_token("", "xyz").offset
            Traceback (most recent call last):
                ...
            ValueError: We need some text to work with.
            >>> lz77_compressor._find_encoding_token("abc", "").offset
            0
        """

        if not text:
            raise ValueError("We need some text to work with.")

        # Initialise result parameters to default values
        length, offset = 0, 0

        if not search_buffer:
            return Token(offset, length, text[length])

        for i, character in enumerate(search_buffer):
            found_offset = len(search_buffer) - i
            if character == text[0]:
                found_length = self._match_length_from_index(text, search_buffer, 0, i)
                # if the found length is bigger than the current or if it's equal,
                # which means it's offset is smaller: update offset and length
                if found_length >= length:
                    offset, length = found_offset, found_length

        return Token(offset, length, text[length])

    def _match_length_from_index(
        self, text: str, window: str, text_index: int, window_index: int