#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @Date : 2018-05-31 21:38:26
# @Author : Zhi Liu (zhiliu.mind@gmail.com)
# @Link : http://iridescent.ink
# @Version : $1.1$
import heapq
import os
from functools import total_ordering
"""
Note: modifided from bhrigu.me's code
Code for Huffman Coding, compression and decompression.
Explanation at http://bhrigu.me/blog/2017/01/17/huffman-coding-python-implementation/
- padded at the end wiyh '0'
- padded length(1Byte) is at the begining of codes.
"""
[docs]@total_ordering
class HeapNode:
def __init__(self, char, freq):
self.char = char
self.freq = freq
self.left = None
self.right = None
# defining comparators less_than and equals
def __lt__(self, other):
return self.freq < other.freq
def __eq__(self, other):
if other is None:
return False
if(not isinstance(other, HeapNode)):
return False
return self.freq == other.freq
[docs]class HuffmanCoding:
def __init__(self, path):
self.path = path
self.heap = []
self.codes = {}
self.reverse_mapping = {}
# functions for compression:
[docs] def make_frequency_dict(self, text):
frequency = {}
for character in text:
if character not in frequency:
frequency[character] = 0
frequency[character] += 1
return frequency
[docs] def make_heap(self, frequency):
for key in frequency:
node = HeapNode(key, frequency[key])
heapq.heappush(self.heap, node)
[docs] def merge_nodes(self):
while(len(self.heap) > 1):
node1 = heapq.heappop(self.heap)
node2 = heapq.heappop(self.heap)
merged = HeapNode(None, node1.freq + node2.freq)
merged.left = node1
merged.right = node2
heapq.heappush(self.heap, merged)
[docs] def make_codes_helper(self, root, current_code):
if root is None:
return
if root.char is not None:
self.codes[root.char] = current_code
self.reverse_mapping[current_code] = root.char
return
self.make_codes_helper(root.left, current_code + "1")
self.make_codes_helper(root.right, current_code + "0")
[docs] def make_codes(self):
root = heapq.heappop(self.heap)
current_code = ""
self.make_codes_helper(root, current_code)
[docs] def get_encoded_text(self, text):
encoded_text = ""
for character in text:
encoded_text += self.codes[character]
return encoded_text
[docs] def pad_encoded_text(self, encoded_text):
extra_padding = 8 - len(encoded_text) % 8
for i in range(extra_padding):
encoded_text += "0"
padded_info = "{0:08b}".format(extra_padding)
encoded_text = padded_info + encoded_text
return encoded_text, padded_info
[docs] def get_byte_array(self, padded_encoded_text):
if(len(padded_encoded_text) % 8 != 0):
print("Encoded text not padded properly")
exit(0)
b = bytearray()
for i in range(0, len(padded_encoded_text), 8):
byte = padded_encoded_text[i:i + 8]
b.append(int(byte, 2))
return b
[docs] def compress(self):
filename, file_extension = os.path.splitext(self.path)
output_path = filename + ".bin"
with open(self.path, 'r+') as file, open(output_path, 'wb') as output:
text = file.read()
print(text)
text = text.rstrip()
print(text)
frequency = self.make_frequency_dict(text)
self.make_heap(frequency)
self.merge_nodes()
self.make_codes()
encoded_text = self.get_encoded_text(text)
padded_encoded_text, padded_info = self.pad_encoded_text(
encoded_text)
b = self.get_byte_array(padded_encoded_text)
print(padded_encoded_text)
output.write(bytes(b))
print("Compressed")
return output_path
""" functions for decompression: """
[docs] def remove_padding(self, padded_encoded_text):
padded_info = padded_encoded_text[:8]
extra_padding = int(padded_info, 2)
padded_encoded_text = padded_encoded_text[8:]
encoded_text = padded_encoded_text[:-1 * extra_padding]
return encoded_text
[docs] def decode_text(self, encoded_text):
current_code = ""
decoded_text = ""
for bit in encoded_text:
current_code += bit
if(current_code in self.reverse_mapping):
character = self.reverse_mapping[current_code]
decoded_text += character
current_code = ""
return decoded_text
[docs] def decompress(self, input_path):
filename, file_extension = os.path.splitext(self.path)
output_path = filename + "_decompressed" + ".txt"
with open(input_path, 'rb') as file, open(output_path, 'w') as output:
bit_string = ""
byte = file.read(1)
while(len(byte) > 0):
byte = ord(byte)
bits = bin(byte)[2:].rjust(8, '0')
bit_string += bits
byte = file.read(1)
encoded_text = self.remove_padding(bit_string)
decompressed_text = self.decode_text(encoded_text)
output.write(decompressed_text)
print("Decompressed")
return output_path