Update lz77.py

compression/lz77.py

@@ -28,38 +28,30 @@
 en.wikipedia.org/wiki/LZ77_and_LZ78
 """
 
-from __future__ import annotations
+
+from dataclasses import dataclass
 
 __version__ = "0.1"
 __author__ = "Lucia Harcekova"
 
 
+@dataclass
 class Token:
  """
  Dataclass representing triplet called token consisting of length, offset
  and indicator. This triplet is used during LZ77 compression.
  """
-
- def __init__(self, offset: int, length: int, indicator: str) -> None:
- self.offset = offset
- self.length = length
- self.indicator = indicator
+ offset: int
+ length: int
+ indicator: str
 
  def __repr__(self) -> str:
  """
- Tests:
- >>> token = Token(5, 6, "a")
- >>> token.__repr__()
- '(5, 6, a)'
- """
- return f"({self.offset}, {self.length}, {self.indicator})"
-
- def __str__(self) -> str:
- """
- Tests:
- >>> token = Token(5, 6, "a")
- >>> token.__str__()
- '(5, 6, a)'
+ >>> token = Token(1, 2, "c")
+ >>> repr(token)
+ '(1, 2, c)'
+ >>> str(token)
+ '(1, 2, c)'
  """
  return f"({self.offset}, {self.length}, {self.indicator})"
 
@@ -75,23 +67,20 @@ def __init__(self, window_size: int = 13, lookahead_buffer_size: int = 6) -> Non
  self.search_buffer_size = self.window_size - self.lookahead_buffer_size
 
  def compress(self, text: str) -> list[Token]:
- """This method compresses given string text using LZ77 compression algorithm.
+ """
+ Compress the given string text using LZ77 compression algorithm.
 
  Args:
- text: string that's going to be compressed
-
- Returns:
- output: the compressed text
+ text: string to be compressed
 
  Returns:
- Compressed text made of triplets (offset, length, indicator).
+ output: the compressed text as a list of Tokens
 
- Tests:
- >>> lz77_compressor = LZ77Compressor(13, 6)
- >>> str(lz77_compressor.compress("ababcbababaa"))
- '[(0, 0, a), (0, 0, b), (2, 2, c), (4, 3, a), (2, 2, a)]'
- >>> str(lz77_compressor.compress("aacaacabcabaaac"))
- '[(0, 0, a), (1, 1, c), (3, 4, b), (3, 3, a), (1, 2, c)]'
+ >>> lz77_compressor = LZ77Compressor()
+ >>> str(lz77_compressor.compress("ababcbababaa"))
+ '[(0, 0, a), (0, 0, b), (2, 2, c), (4, 3, a), (2, 2, a)]'
+ >>> str(lz77_compressor.compress("aacaacabcabaaac"))
+ '[(0, 0, a), (1, 1, c), (3, 4, b), (3, 3, a), (1, 2, c)]'
  """
 
  output = []
@@ -121,8 +110,8 @@ def compress(self, text: str) -> list[Token]:
  return output
 
  def decompress(self, tokens: list[Token]) -> str:
- """This method turns the list of tokens consisting of triplets of the form
- (offset, length, char), into an output string.
+ """
+ Convert the list of tokens into an output string.
 
  Args:
  tokens: list containing triplets (offset, length, char)
@@ -131,16 +120,16 @@ def decompress(self, tokens: list[Token]) -> str:
  output: decompressed text
 
  Tests:
- >>> lz77_compressor = LZ77Compressor(13, 6)
- >>> lz77_compressor.decompress([Token(0, 0, 'c'), Token(0, 0, 'a'), \
-  Token(0, 0, 'b'), Token(0, 0, 'r'), Token(3, 1, 'c'), \
-   Token(2, 1, 'd'), Token(7, 4, 'r'), Token(3, 5, 'd')])
+ >>> lz77_compressor = LZ77Compressor()
+ >>> lz77_compressor.decompress([Token(0, 0, 'c'), Token(0, 0, 'a'),
+ ... Token(0, 0, 'b'), Token(0, 0, 'r'), Token(3, 1, 'c'),
+ ... Token(2, 1, 'd'), Token(7, 4, 'r'), Token(3, 5, 'd')])
  'cabracadabrarrarrad'
- >>> lz77_compressor.decompress([Token(0, 0, 'a'), Token(0, 0, 'b'), \
-   Token(2, 2, 'c'), Token(4, 3, 'a'), Token(2, 2, 'a')])
+ >>> lz77_compressor.decompress([Token(0, 0, 'a'), Token(0, 0, 'b'),
+ ... Token(2, 2, 'c'), Token(4, 3, 'a'), Token(2, 2, 'a')])
  'ababcbababaa'
- >>> lz77_compressor.decompress([Token(0, 0, 'a'), Token(1, 1, 'c'), \
-   Token(3, 4, 'b'), Token(3, 3, 'a'), Token(1, 2, 'c')])
+ >>> lz77_compressor.decompress([Token(0, 0, 'a'), Token(1, 1, 'c'),
+ ... Token(3, 4, 'b'), Token(3, 3, 'a'), Token(1, 2, 'c')])
  'aacaacabcabaaac'
  """
 
@@ -157,17 +146,28 @@ 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(13, 6)
+ >>> 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 search_buffer == "":
+ if not search_buffer:
  return Token(offset, length, text[length])
 
  for i, character in enumerate(search_buffer):
@@ -200,19 +200,21 @@ def _match_length_from_index(
  >>> lz77_compressor = LZ77Compressor(13, 6)
  >>> lz77_compressor._match_length_from_index("rarrad", "adabrar", 0, 4)
  5
- >>> lz77_compressor._match_length_from_index("adabrarrarrad", \
-   "cabrac", 0, 1)
+ >>> lz77_compressor._match_length_from_index("adabrarrarrad",
+ ... "cabrac", 0, 1)
  1
  """
- if text == "" or text[text_index] != window[window_index]:
+ if not text or text[text_index] != window[window_index]:
  return 0
  return 1 + self._match_length_from_index(
  text, window + text[text_index], text_index + 1, window_index + 1
  )
 
 
 if __name__ == "__main__":
+ from doctest import testmod
 
+ testmod()
  # Initialize compressor class
  lz77_compressor = LZ77Compressor(window_size=13, lookahead_buffer_size=6)