Python/compression/lempel_ziv_decompress.py
Christian Clauss 9b95e4f662
Pyupgrade to python3.8 ()
* Upgrade to Python 3.8 syntax

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
2020-10-21 12:46:14 +02:00

112 lines
3.1 KiB
Python
Raw Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

"""
One of the several implementations of LempelZivWelch decompression algorithm
https://en.wikipedia.org/wiki/Lempel%E2%80%93Ziv%E2%80%93Welch
"""
import math
import sys
def read_file_binary(file_path: str) -> str:
"""
Reads given file as bytes and returns them as a long string
"""
result = ""
try:
with open(file_path, "rb") as binary_file:
data = binary_file.read()
for dat in data:
curr_byte = f"{dat:08b}"
result += curr_byte
return result
except OSError:
print("File not accessible")
sys.exit()
def decompress_data(data_bits: str) -> str:
"""
Decompresses given data_bits using LempelZivWelch compression algorithm
and returns the result as a string
"""
lexicon = {"0": "0", "1": "1"}
result, curr_string = "", ""
index = len(lexicon)
for i in range(len(data_bits)):
curr_string += data_bits[i]
if curr_string not in lexicon:
continue
last_match_id = lexicon[curr_string]
result += last_match_id
lexicon[curr_string] = last_match_id + "0"
if math.log2(index).is_integer():
newLex = {}
for curr_key in list(lexicon):
newLex["0" + curr_key] = lexicon.pop(curr_key)
lexicon = newLex
lexicon[bin(index)[2:]] = last_match_id + "1"
index += 1
curr_string = ""
return result
def write_file_binary(file_path: str, to_write: str) -> None:
"""
Writes given to_write string (should only consist of 0's and 1's) as bytes in the
file
"""
byte_length = 8
try:
with open(file_path, "wb") as opened_file:
result_byte_array = [
to_write[i : i + byte_length]
for i in range(0, len(to_write), byte_length)
]
if len(result_byte_array[-1]) % byte_length == 0:
result_byte_array.append("10000000")
else:
result_byte_array[-1] += "1" + "0" * (
byte_length - len(result_byte_array[-1]) - 1
)
for elem in result_byte_array[:-1]:
opened_file.write(int(elem, 2).to_bytes(1, byteorder="big"))
except OSError:
print("File not accessible")
sys.exit()
def remove_prefix(data_bits: str) -> str:
"""
Removes size prefix, that compressed file should have
Returns the result
"""
counter = 0
for letter in data_bits:
if letter == "1":
break
counter += 1
data_bits = data_bits[counter:]
data_bits = data_bits[counter + 1 :]
return data_bits
def compress(source_path: str, destination_path: str) -> None:
"""
Reads source file, decompresses it and writes the result in destination file
"""
data_bits = read_file_binary(source_path)
data_bits = remove_prefix(data_bits)
decompressed = decompress_data(data_bits)
write_file_binary(destination_path, decompressed)
if __name__ == "__main__":
compress(sys.argv[1], sys.argv[2])