mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-11-24 05:21:09 +00:00
19b713aecb
* Added lempel-ziv compression algorithm implementation * Added lempel-ziv decompression algorithm implementation * Reformatted lempel-ziv compress/decompress files using black * Added type hints and some other modifications (Doctests coming up) * Shortened several lines to comply with the standards
112 lines
3.1 KiB
Python
112 lines
3.1 KiB
Python
"""
|
||
One of the several implementations of Lempel–Ziv–Welch 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 = "{0:08b}".format(dat)
|
||
result += curr_byte
|
||
return result
|
||
except IOError:
|
||
print("File not accessible")
|
||
sys.exit()
|
||
|
||
|
||
def decompress_data(data_bits: str) -> str:
|
||
"""
|
||
Decompresses given data_bits using Lempel–Ziv–Welch 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 IOError:
|
||
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])
|